Fixed the issue that dirname: META got zipped twice.

When building target-files-package, dir: META has to be copied first
to help early validation of the .zip file.

In order to prevent $(zip_root)/META from getting copied twice to $@.list,
use the method (find -path -prune -o -print) instead of (grep pattern -v).

Test: m target-files-package
Bug: b/31676493
Change-Id: Id6b4d77fb62aa136253de88573cc51a575b90be2