Delete most network scorer tests from coretests.

Anything which tests public API functionality will be moved to a
compatibility test suite.

The only remaining test is NetworkScorerAppManagerTest, which contains
unit tests for an internal helper class that is not (and should not
be) exposed via @SystemApi or otherwise.

Bug: 16355542
Change-Id: I478da97d3a4d09407992af37e45466dc484fa8cf