Do not enable the Content Protection toggle for non-admin users.

Flag: EXEMPT bugfix
Bug: 409318132
Test: m -j256 Settings && atest
SettingsRoboTests:ContentProtectionTogglePreferenceControllerTest
(cherry picked from commit ef801e1a8ec3a18ce9e0221fc7e1dfe495d0be8a)
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:077aae694d85f7e1f2919977b15c19c7f21b1da2)
Merged-In: I46609c795923d427a5b7fa10bc2e8b071fad72d6
Change-Id: I46609c795923d427a5b7fa10bc2e8b071fad72d6