PHPC-2477: MONGOC_ENABLE_SASL_GSSAPI is obsolete

CDRIVER-2654 removed MONGOC_ENABLE_SASL_GSSAPI. PHPC-2312 removed it from Autotools, but it was left behind in config.w32.

Author: jmikola

config.w32

@@ -175,7 +175,6 @@ if (PHP_MONGODB != "no") {
     MONGOC_ENABLE_MONGODB_AWS_AUTH: 0,
     MONGOC_ENABLE_SASL: 0,
     MONGOC_ENABLE_SASL_CYRUS: 0,
-    MONGOC_ENABLE_SASL_GSSAPI: 0,
     MONGOC_ENABLE_SASL_SSPI: 0,
     MONGOC_ENABLE_SRV: 0,
     MONGOC_ENABLE_RDTSCP: 0,