Revert "Expose ACTION_USER_SWITCHED as system API"
This reverts commit ffe0cbe5.
Reason for revert: Not needed for now; will be redone in S.
Bug: 148180958
Merged-in: I426e00e1eb79af5b520fc8c59439614459720fa6
Change-Id: I426e00e1eb79af5b520fc8c59439614459720fa6
(cherry picked from commit 5a29b044)