contrib: remove unneeded gecko

contrib/src/gecko/rules.mak

-# gecko (mozilla plugin headers)
-
-PKGS += gecko
-
-NPAPI_HEADERS_SVN_URL := http://npapi-sdk.googlecode.com/svn/trunk/headers
-NPAPI_HEADERS_SVN_REV := HEAD # revision number, or just HEAD for the latest
-
-$(TARBALLS)/gecko-svn.tar.xz:
-	rm -Rf gecko-svn
-	$(SVN) export $(NPAPI_HEADERS_SVN_URL) gecko-svn -r $(NPAPI_HEADERS_SVN_REV)
-	tar cvJ gecko-svn > $@
-
-.sum-gecko: gecko-svn.tar.xz
-	$(warning Integrity check skipped.)
-	touch $@
-
-gecko: gecko-svn.tar.xz .sum-gecko
-	$(UNPACK)
-	$(MOVE)
-
-.gecko: gecko
-	cp $</*.h "$(PREFIX)/include"
-	touch $@