Revert "Start NearbyService when system server starts."

This reverts commit 0fc06be8.

Reason for revert: The original change is fine, but is not be
necessary anymore once the service is started from the
Connectivity initializer. This is to be submitted together with
changes achieving that.

Bug: 189355156
Bug: 214495869
Test: check service started from new path
Change-Id: I26e1a89522f7a8ce72e7576a1f2f697845eef617