Fix for incorrect proximity alert interval setting

LOCATION_BACKGROUND_THROTTLE_PROXIMITY_ALERT_INTERVAL_MS
should be used as the value for proximity alert interval.
However, LOCATION_BACKGROUND_THROTTLE_INTERVAL_MS is used
instead.

Bug: 64937144
Bug: 36197768
Test: manual
Change-Id: I589c5eecc2f331992cd057364b472afeb8bde756