Make ContextualSearchInvoker not a ResourceBasedOverride.

This was previously only used to honor the INVOKE_OMNI_LPH flag
which has been enabled for a long time. So this is part of that
cleanup.

Bug: 297561673
Test: Manual
Flag: EXEMPT deleting legacy flag
Change-Id: Ife9f14faa2099f579f631da2aadaa6a56cbba51d