Enable latency metrics

The metrics were disabled in S because the WeakReference bugs could not
be fixed in time.

Enable them in T, which should allow sufficient time for the other teams
to resolve the WeakReference problems.

Bug: 169866723
Test: adb shell dumpsys input, watch for latency tracker starting to
collect data

Change-Id: I67c4028e7cb8b5e26616ab90b8b60fc871bf4407