Avoid fake enums in test.

Were these ever used, this would have been an error.

tests/run/cpdef_enums.pxd

 cdef extern from *:
-    cpdef enum ExternPxdEnum:
+    cpdef enum: # ExternPxd
         FOUR "4"
         EIGHT "8"
 
-    cdef enum ExternSecretPxdEnum:
+    cdef enum: # ExternSecretPxd
         SIXTEEN "16"
 
 cpdef enum PxdEnum:

tests/run/cpdef_enums.pyx

@@ -26,12 +26,12 @@ NameError: ...name 'RANK_3' is not defined
 
 
 cdef extern from *:
-    cpdef enum ExternPyxEnum:
+    cpdef enum: # ExternPyx
         ONE "1"
         TEN "10"
         HUNDRED "100"
 
-    cdef enum ExternSecretPyxEnum:
+    cdef enum: # ExternSecretPyx
         THOUSAND "1000"
 
 cpdef enum PyxEnum: