free: instead of Curl_safefree()

Since we just started make use of free(NULL) in order to simplify code,
this change takes it a step further and:

- converts lots of Curl_safefree() calls to good old free()
- makes Curl_safefree() not check the pointer before free()

The (new) rule of thumb is: if you really want a function call that
frees a pointer and then assigns it to NULL, then use Curl_safefree().
But we will prefer just using free() from now on.

lib/curl_ntlm_core.c

@@ -618,7 +618,7 @@ CURLcode Curl_ntlm_core_mk_ntlmv2_hash(const char *user, size_t userlen,
   result = Curl_hmac_md5(ntlmhash, 16, identity, curlx_uztoui(identity_len),
                          ntlmv2hash);
 
-  Curl_safefree(identity);
+  free(identity);
 
   return result;
 }
@@ -705,8 +705,7 @@ CURLcode Curl_ntlm_core_mk_ntlmv2_resp(unsigned char *ntlmv2hash,
   result = Curl_hmac_md5(ntlmv2hash, NTLM_HMAC_MD5_LEN, ptr + 8,
                          NTLMv2_BLOB_LEN + 8, hmac_output);
   if(result) {
-    Curl_safefree(ptr);
-
+    free(ptr);
     return result;
   }