gd: Cleanup up old test sources :BluetoothHciTestSources

The filegroup :BluetoothHciTestSources was neither being
compiled nor run.

- Remove duplicate test files "le_advertising_manager_test.cc",
  "le_scanning_manager_test.cc", already compiled in
  :BluetoothHciUnitTestSources
- Remove duplicate tests in hci_layer_test.cc: new tests were
  implemented in hci_layer_unittest.cc, move remaining tests
  to hci_layer_unittest.cc
- Move all remaining files to :bluetoothHciUnitTestSources and
  fix compilation issues

This change leaves 4 tests disabled:
  HciTest.HciTimeOut
  LeAddressManagerTest.rotator_address_for_multiple_client
  StackManagerTest.start_and_shutdown_no_module
  StackManagerTest.get_module_instance

Test: atest --host bluetooth_test_gd_unit
Change-Id: I3ebd4d70c7d3449ff0983e4af0f20bde205e701a