Revert "Move SettingsProxyExt content observer registration call on bg thread."

This reverts commit 0ccaa029c98b89c68c989b0b0436b63157c58acf.

Reason for revert: Droidmonitor triggered revert due to b/357575679.

Change-Id: Icbe8ba2723b1d2a44ce4d3853ef2cfcb5360039a
3 files changed