Make IActivityManager.killPids asynchronized

Currently it's only used by WMS, and the caller has held other locks
before calling into this interface in which it'll require to acquire
the AMS lock and thus results in potential deadlocks.

Now making it asynchronized to untangle the locks here.

BYPASS_INCLUSIVE_LANGUAGE_REASON=Legacy API name

Bug: 188793757
Test: atest FrameworksServicesTests
Change-Id: I5d1405eb3ef55ad683602335acebc78ff7e8d4c9