debian: remove .skip flags on clean target.

debian/Makefile

diff --git a/debian/Makefile b/debian/Makefile
index 0496c49..d7b13ad 100644
--- a/debian/Makefile
+++ b/debian/Makefile
@@ -428,7 +428,7 @@
 
 clean:
 	@rm -rf base module-* rules-base rules-module-* debuild-base debuild-module-* nginx-tests $(BASE_SRC) .deps-module-*
-	@rm -f nginx.deb-changelog nginx-module-*.deb-changelog
+	@rm -f nginx.deb-changelog nginx-module-*.deb-changelog nginx-module-*.skip
 
 .PHONY:	default list list-base list-all-modules list-base-modules all modules rules test test-debug clean