stop overwriting make uninstall

Makefile.coq.local

-uninstall::
-	@# This makes sure we also delete stale files in the destination directory
-	$(HIDE)df="$(COQLIBINSTALL)/`$(COQMKFILE) -destination-of "theories/base.v" $(COQLIBS)`" &&\
-	echo "RM in $$df" &&\
-	if [ -d "$$df" ]; then find "$$df" \( -name "*.vo" -o -name "*.v" -o -name "*.glob" -o \( -type d -empty \) \) -print -delete; fi