Revert "Makefile: add target to print generated files"

This reverts commit 9578f8cc.

The patch snuck in by accident without having been posted to
qemu-devel.  It's entirely redundant: existing target print-% already
serves the purpose.

Cc: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: NMarkus Armbruster <armbru@redhat.com>
Message-Id: <20180504054241.6833-1-armbru@redhat.com>
Reviewed-by: NEric Blake <eblake@redhat.com>

Makefile

@@ -1055,9 +1055,6 @@ endif
 include $(SRC_PATH)/tests/docker/Makefile.include
 include $(SRC_PATH)/tests/vm/Makefile.include
 
-printgen:
-	@echo $(GENERATED_FILES)
-
 .PHONY: help
 help:
 	@echo  'Generic targets:'