contrib: mad: remove forced -O3

This shouldn't be enforced. We already use -O2 on release builds.

-O4 was removed in 8d098023
-O3 was added with the contrib in 9c0b836a

contrib/src/mad/rules.mak

@@ -19,7 +19,7 @@ endif
 $(TARBALLS)/libmad-$(MAD_VERSION).tar.gz:
 	$(call download,$(MAD_URL))
 
-LIBMAD_VARS := CFLAGS="$(CFLAGS) -O3"
+LIBMAD_VARS :=
 ifdef HAVE_IOS
 LIBMAD_VARS += CCAS="$(AS)"
 endif