mysqlnd: Remove unnecessary check for HAVE_ZLIB

If MYSQLND_COMPRESSION_WANTED is set, we already guarantee that
zlib is linked, but don't necessarily set HAVE_ZLIB.

Closes GH-5658.

Author: talyz

ext/mysqlnd/mysqlnd.h

@@ -48,7 +48,7 @@
 #define MYSQLND_DBG_ENABLED 0
 #endif
 
-#if defined(MYSQLND_COMPRESSION_WANTED) && defined(HAVE_ZLIB)
+#if defined(MYSQLND_COMPRESSION_WANTED)
 #define MYSQLND_COMPRESSION_ENABLED 1
 #endif