Rename NetworkStackPermissionStub

Use NetworkStackPermissionConfig instead.
Also remove the source directory: soong now manages to build the package
without it.

Bug: 129317412
Test: Flashed, booted, WiFi working
(clean cherry-pick of aosp I45299c12598cd3b33bfd78ae8698d98b77b18dc0)

Change-Id: I7bdc058dddfa483823074055ad5c9d7d2efd37b9