Fix potential deadlock in measurements report

If Gnss Measurements callback is called at the same time
as Gnss Measurements close is called, this will cause
dead lock.
Remove using mutex in this case and instead use a simple
bool to know whether or not to call into a the callback.

Bug: 63909793
Change-Id: I98d2be5ebd2ee0f36e4d2e31d20a74585089fe31
CRs-fixed: 2089716
2 files changed