Revert "[metrics] Always enable background thread"

This reverts commit 6660e3bd463535ea6aefebc3288ac3f17fbd99fd.

Bug: 170149255

Reason for revert: Test ThreadLifecycleCallbackJava flakey.

Change-Id: Ib118654c414c27bd71d7ad3e19e1fab2d06347c7
5 files changed