Correct visibility for LOCATION_MODE_ON

As per API feedback in b/126727563, move LOCATION_MODE_ON to SystemApi
instead of deprecated. This is safe as this constant is not used
anywhere yet.

Test: manual
Bug: 126727563
Change-Id: Iddbea546d1585cb8677c4adb97e465d5ac7a76a4
Merged-In: Iddbea546d1585cb8677c4adb97e465d5ac7a76a4
(cherry picked from commit 74491089)