Revert "Add clean-diff that runs fix_diffs.py for every changed po files"

This reverts commit c330bcb.

Author: adrianliaw

Makefile

@@ -101,7 +101,3 @@ fuzzy:
 .PHONY: clean
 clean:
 	rm *.mo */*.mo
-
-.PHONY: clean-diff
-clean-diff: $(VENV)/bin/activate
-	for file in $$(git diff --name-only | grep '.po$$'); do python3 scripts/fix_diffs.py $$file; done