Prevent LocalService#updateOomAdj been called during test

When testing, we mock WindowProcessController#mOwner as Object, if
updateOomAdj is called during test, then the test process will crash.
This won't happen in normal use.
To prevent the test process from crash, mock out ATMS#updateOomAdj()
during test.

Fix: 138770685
Test: atest WmTests
Change-Id: Ibc8e56e6fd9b332d987c7cd2ed501aba4394f7a2