Fix an extraneous parentheses warning.

"if (G_UNLIKELY(...))" triggers an extraneous parentheses warning when
compiling with XCode's clang-500.2.75. From looking at the macro
definition we *should* be able to get rid of the outer parentheses
everywhere.

Change-Id: I710e1cc391e1167c1243c4ddb032f2831f0a9498
Reviewed-on: https://code.wireshark.org/review/1432
Reviewed-by: Gerald Combs <gerald@wireshark.org>

epan/wmem/wmem_map.c

@@ -36,7 +36,7 @@ void
 wmem_init_hashing(void)
 {
     x = g_random_int();
-    if (G_UNLIKELY(x == 0))
+    if G_UNLIKELY(x == 0)
         x = 1;
 
     preseed  = g_random_int();