bpo-36459: Fix a possible double PyMem_FREE() due to tokenizer.c's tok_nextc() (12601)

Remove the PyMem_FREE() call added in cb90c89d.  The buffer will be
freed when PyTokenizer_Free() is called on the tokenizer state.
(cherry picked from commit cda139d1)
Co-authored-by: Zackery Spytz <zspytz@gmail.com>

Misc/NEWS.d/next/Core and Builtins/2019-03-27-22-35-16.bpo-36459.UAvkKp.rst

+Fix a possible double ``PyMem_FREE()`` due to tokenizer.c's ``tok_nextc()``.

Parser/tokenizer.c

@@ -979,7 +979,6 @@ tok_nextc(register struct tok_state *tok)
                 newbuf = (char *)PyMem_REALLOC(newbuf,
                                                newsize);
                 if (newbuf == NULL) {
-                    PyMem_FREE(tok->buf);
                     tok->done = E_NOMEM;
                     tok->cur = tok->inp;
                     return EOF;