Follow-up of #3773: In PyTokenizer_FindEncoding, remove the call to PyErr_NoMemory when PyMem_MALLOC() fails.

It is not stritly necessary, the function may already return NULL without an exception set,
for example when the file cannot be opened.

Discussed with Benjamin Peterson.

Parser/tokenizer.c

@@ -1612,8 +1612,6 @@ PyTokenizer_FindEncoding(int fd)
             encoding = (char *)PyMem_MALLOC(strlen(tok->encoding) + 1);
             if (encoding)
                 strcpy(encoding, tok->encoding);
-            else
-                PyErr_NoMemory();
         }
 	PyTokenizer_Free(tok);
 	return encoding;