Disable trimMemory(BACKGROUND) on lock with a Flag

Issuing this trim level causes a massive leak on DMA heap where surfaces
get allocated on each unlock.

We need to fix underlying issue there before we can reenable the flag.

Bug:282816553
Bug:275486055

Test: atest ResourceTrimmerTest
Change-Id: I6eaa5f0aa1f56e2ff5c6345bef7d78b5a648a571