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)
1 file changed