Enforce system privilege for getGlobalProxyAdmin getGlobalProxyAdmin is a hidden API and called just from Settings. So enforcing system uid check. Bug: 206127671 Test: NA Change-Id: Id4bce828bc69867c9c4d20b991e9e53e8ae385f2 Merged-In: Id4bce828bc69867c9c4d20b991e9e53e8ae385f2 (cherry picked from commit 554e19a375bb3c61db7643b17ea411baf6bbe3e5)