Remove the outdated getbuffer/releasebuffer implementations for the NumPy...

Remove the outdated getbuffer/releasebuffer implementations for the NumPy 'ndarray' since there are probably no NumPy installations out there anymore that do not support the buffer protocol themselves and are still worth supporting.

See https://github.com/numpy/numpy/pull/12284#discussion_r420378155
See GH-3573

Cython/Includes/numpy/__init__.pxd

@@ -281,97 +281,6 @@ cdef extern from "numpy/arrayobject.h":
                 """
                 return PyArray_BYTES(self)
 
-
-        # Note: This syntax (function definition in pxd files) is an
-        # experimental exception made for __getbuffer__ and __releasebuffer__
-        # -- the details of this may change.
-        def __getbuffer__(ndarray self, Py_buffer* info, int flags):
-            # This implementation of getbuffer is geared towards Cython
-            # requirements, and does not yet fulfill the PEP.
-            # In particular strided access is always provided regardless
-            # of flags
-
-            cdef int i, ndim
-            cdef int endian_detector = 1
-            cdef bint little_endian = ((<char*>&endian_detector)[0] != 0)
-
-            ndim = PyArray_NDIM(self)
-
-            if ((flags & pybuf.PyBUF_C_CONTIGUOUS == pybuf.PyBUF_C_CONTIGUOUS)
-                and not PyArray_CHKFLAGS(self, NPY_ARRAY_C_CONTIGUOUS)):
-                raise ValueError(u"ndarray is not C contiguous")
-
-            if ((flags & pybuf.PyBUF_F_CONTIGUOUS == pybuf.PyBUF_F_CONTIGUOUS)
-                and not PyArray_CHKFLAGS(self, NPY_ARRAY_F_CONTIGUOUS)):
-                raise ValueError(u"ndarray is not Fortran contiguous")
-
-            info.buf = PyArray_DATA(self)
-            info.ndim = ndim
-            if sizeof(npy_intp) != sizeof(Py_ssize_t):
-                # Allocate new buffer for strides and shape info.
-                # This is allocated as one block, strides first.
-                info.strides = <Py_ssize_t*>PyObject_Malloc(sizeof(Py_ssize_t) * 2 * <size_t>ndim)
-                info.shape = info.strides + ndim
-                for i in range(ndim):
-                    info.strides[i] = PyArray_STRIDES(self)[i]
-                    info.shape[i] = PyArray_DIMS(self)[i]
-            else:
-                info.strides = <Py_ssize_t*>PyArray_STRIDES(self)
-                info.shape = <Py_ssize_t*>PyArray_DIMS(self)
-            info.suboffsets = NULL
-            info.itemsize = PyArray_ITEMSIZE(self)
-            info.readonly = not PyArray_ISWRITEABLE(self)
-
-            cdef int t
-            cdef char* f = NULL
-            cdef dtype descr = <dtype>PyArray_DESCR(self)
-            cdef int offset
-
-            info.obj = self
-
-            if not PyDataType_HASFIELDS(descr):
-                t = descr.type_num
-                if ((descr.byteorder == c'>' and little_endian) or
-                    (descr.byteorder == c'<' and not little_endian)):
-                    raise ValueError(u"Non-native byte order not supported")
-                if   t == NPY_BYTE:        f = "b"
-                elif t == NPY_UBYTE:       f = "B"
-                elif t == NPY_SHORT:       f = "h"
-                elif t == NPY_USHORT:      f = "H"
-                elif t == NPY_INT:         f = "i"
-                elif t == NPY_UINT:        f = "I"
-                elif t == NPY_LONG:        f = "l"
-                elif t == NPY_ULONG:       f = "L"
-                elif t == NPY_LONGLONG:    f = "q"
-                elif t == NPY_ULONGLONG:   f = "Q"
-                elif t == NPY_FLOAT:       f = "f"
-                elif t == NPY_DOUBLE:      f = "d"
-                elif t == NPY_LONGDOUBLE:  f = "g"
-                elif t == NPY_CFLOAT:      f = "Zf"
-                elif t == NPY_CDOUBLE:     f = "Zd"
-                elif t == NPY_CLONGDOUBLE: f = "Zg"
-                elif t == NPY_OBJECT:      f = "O"
-                else:
-                    raise ValueError(u"unknown dtype code in numpy.pxd (%d)" % t)
-                info.format = f
-                return
-            else:
-                info.format = <char*>PyObject_Malloc(_buffer_format_string_len)
-                info.format[0] = c'^' # Native data types, manual alignment
-                offset = 0
-                f = _util_dtypestring(descr, info.format + 1,
-                                      info.format + _buffer_format_string_len,
-                                      &offset)
-                f[0] = c'\0' # Terminate format string
-
-        def __releasebuffer__(ndarray self, Py_buffer* info):
-            if PyArray_HASFIELDS(self):
-                PyObject_Free(info.format)
-            if sizeof(npy_intp) != sizeof(Py_ssize_t):
-                PyObject_Free(info.strides)
-                # info.shape was stored after info.strides in the same block
-
-
     ctypedef unsigned char      npy_bool
 
     ctypedef signed char      npy_byte