Clean up old shim from private-space integration

At the time of the initial integration, `ResolveInfo.userHandle`
didn't exist / wasn't guaranteed to be populated, and this shim let
us prepare to use that property once it was available while falling
back on some placeholder value. That transition is now complete, so
this CL inlines the shim implementation everywhere it was called.

This is a trivial refactoring.

Bug: 364732048
Test: Build/presubmit
Flag: EXEMPT refactor
Change-Id: I770ef54614e838eb4af83c2d319661380cf9ff6f