Fix NetworkScorerAppManager#isCallerActiveScorer.

The current implementation checks whether the caller's uid has the
SCORE_NETWORKS permission instead of checking the passed in callingUid. I
removed this check entirely because the getActiveScorer method already checks
whether the scorer's package has the SCORE_NETWORKS permission. There is no way
callingUid can equal the active scoring package's uid without also having the
SCORE_NETWORKS permission.

Bug: 34107721
Test: runtest --path core/tests/coretests/src/android/net/NetworkScorerAppManagerTest.java
Change-Id: Ifd427792169837c84a10a76b208c76137db06ae9