Revert "Post creating the `android.bg` thread during app start up time for CCAPI use cases."

This reverts commit 538e5354.

Reason for revert: Some behavior was not gated by the flag, and there
are observed performance regressions. See b/392644058.

Bug: 392644058
Change-Id: I04d5866d1ed2902cee4632ca09071fe2e6115c7b