core: applying file overrides from RPM header should be aware of dropped files

[lucab]

Currently rpm-ostree supports omitting files from RPM packages via treefile fields such as remove-from-packages.

However rpm-ostree still tries to applies file overrides on such content, in order to tweak ownership or permission bits. This thus fails because the filepath does not actually exist where expected, in this portion of code: https://github.com/coreos/rpm-ostree/blob/6fb417fb4c31a2a29223418bc8f472d92f6b3085/src/libpriv/rpmostree-core.cxx#L3624-L3633

To fix this, we should make apply_rpmfi_overrides() aware of treefile configuration.

Ref: https://github.com/coreos/fedora-coreos-config/pull/1887#issuecomment-1208292479