Avoid NPE in GpsLocationProvider

Oops, looks like we were spinning up a secondary thread to run some
tasks that will just happen on the main thread regardless. Removed
the secondary thread and fixed up initialisation order regarding
mHandler and things that post to it. Also reordered GPS and
PASSIVE provider initialisation order since GPS depends on PASSIVE.

This should be both safer and easier to read.

Bug: 7248029
Change-Id: I8630caf0a7bd1b2c401603075676f13dda5be4fa