Remove lib/Makefile.libcommon

Reviewed-by: iustinp

lib/Makefile.libcommon

-# We need to create symlinks because "make distcheck" will not install Python
-# files for building.
-pre-check: all
-	for i in $(python_files); do \
-		if test ! -f $$i; then \
-			$(LN_S) $(srcdir)/$$i $$i; \
-		fi; \
-	done