Removed the unsafe nxt_memcmp() wrapper for memcmp(3).

The casts are unnecessary, since memcmp(3)'s arguments are 'void *'.
It might have been necessary in the times of K&R, where 'void *' didn't
exist.  Nowadays, it's unnecessary, and _very_ unsafe, since casts can
hide all classes of bugs by silencing most compiler warnings.

The changes from nxt_memcmp() to memcmp(3) were scripted:

$ find src/ -type f \
  | grep '\.[ch]$' \
  | xargs sed -i 's/nxt_memcmp/memcmp/'

Reviewed-by: Andrew Clayton <a.clayton@nginx.com>
Signed-off-by: Alejandro Colomar <alx@nginx.com>

src/nxt_openssl.c

@@ -780,7 +780,7 @@ nxt_tls_ticket_key_callback(SSL *s, unsigned char *name, unsigned char *iv,
         /* decrypt session ticket */
 
         do {
-            if (nxt_memcmp(name, ticket[i].name, 16) == 0) {
+            if (memcmp(name, ticket[i].name, 16) == 0) {
                 goto found;
             }