Remove redundant memory.h file

The memory.h file is part of the pre-C89 era and is on today's systems
only a simple wrapper for including the final string.h header file.

ext/mbstring/libmbfl/mbfl/mbfl_allocators.c

@@ -33,11 +33,6 @@
 #endif
 
 #include <stdlib.h>
-
-#ifdef HAVE_MEMORY_H
-#include <memory.h>
-#endif
-
 #include <string.h>
 #include <stddef.h>
 

win32/sendmail.c

@@ -26,7 +26,6 @@
 #include <string.h>
 #include <math.h>
 #include <malloc.h>
-#include <memory.h>
 #include <winbase.h>
 #include "sendmail.h"
 #include "php_ini.h"