MINOR: pattern: use trim_all_pools() instead of a conditional malloc_trim()

First this will ensure that we serialize the threads and avoid severe
contention. Second it removes ugly ifdefs and conditions.
diff --git a/src/pattern.c b/src/pattern.c
index 71f25a4..6c263be 100644
--- a/src/pattern.c
+++ b/src/pattern.c
@@ -2083,11 +2083,8 @@
 	list_for_each_entry(expr, &ref->pat, list)
 		HA_RWLOCK_WRUNLOCK(PATEXP_LOCK, &expr->lock);
 
-#if defined(HA_HAVE_MALLOC_TRIM)
-	if (done && is_trim_enabled()) {
-		malloc_trim(0);
-	}
-#endif
+	if (done)
+		trim_all_pools();
 
 	return done;
 }