Revert "[metrics] Add background reporting thread"

This reverts commit 77f7eb9d05b6d05531556882d99ed63688c6e3b0.

Reason for revert: We're seeing consistent 2233-metrics-background-thread failures on target.

Change-Id: Ie394dbe90289b1472ac4c8876d01ece347541852
14 files changed