contrib: fix regex target

don't assume the system has it (and thus skip building it)
(cherry picked from commit 3082f245)
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

contrib/src/regex/rules.mak

@@ -2,8 +2,6 @@
 REGEX_VERSION := 0.12
 REGEX_URL := http://ftp.gnu.org/old-gnu/regex/regex-$(REGEX_VERSION).tar.gz
 
-PKGS_FOUND += regex
-
 $(TARBALLS)/regex-$(REGEX_VERSION).tar.gz:
 	$(call download,$(REGEX_URL))