Update clean-generated to remove all generated files

Signed-off-by: Nelo-T. Wallus <[email protected]>

Author: ntnn

Makefile

@@ -79,4 +79,5 @@ verify: verify-codegen
 
 .PHONY: clean-generated
 clean-generated:
-	grep --exclude Makefile -l 'Code generated by kcp code-generator. DO NOT EDIT.' -r . | xargs rm
+	grep --exclude Makefile -l -e 'Code generated by [a-z-]*. DO NOT EDIT.' -r . | xargs rm -f
+	find . -type d -empty -delete