Fix build error on AIX, which won't allow 'redefining' of functions (i.e memcopy)

I talked this over with Nisheeth and the only reason this was put in was to
fix compiler warnings.

expat/xmltok/xmldef.h

@@ -60,9 +60,6 @@ particular environments. */
 #define realloc(x, y) PR_Realloc((x), (size_t)(y))
 #define calloc(x, y) PR_Calloc((x),(y))
 #define free(x) PR_Free(x)
-#define memcpy(x, y, z) memcpy((x), (y), (size_t)(z))
-#define memmove(x, y, z) memmove((x), (y), (size_t)(z))
-#define memcmp(x, y, z) memcmp((x), (y), (size_t)(z))
 
 #if PR_BYTES_PER_INT != 4
 typedef PRInt32 int;

parser/expat/lib/xmldef.h

@@ -60,9 +60,6 @@ particular environments. */
 #define realloc(x, y) PR_Realloc((x), (size_t)(y))
 #define calloc(x, y) PR_Calloc((x),(y))
 #define free(x) PR_Free(x)
-#define memcpy(x, y, z) memcpy((x), (y), (size_t)(z))
-#define memmove(x, y, z) memmove((x), (y), (size_t)(z))
-#define memcmp(x, y, z) memcmp((x), (y), (size_t)(z))
 
 #if PR_BYTES_PER_INT != 4
 typedef PRInt32 int;