[Settings] Remove REQUEST_INSTALL_PACKAGES from manifest

This line was initially added to support unarchiving, but it wasn't
necessary because the Settings app already has INSTALL_PACKAGES
permission.

Having REQUEST_INSTALL_PACKAGES causes it to be listed in
the "Install unknown apps" page, which might be confusing to the users.
This CL removes it.

BUG: 304255818
Test: manual with Archive/Restore
Change-Id: Iebead9c0faf0226046784add271c155fb89a0845