Disable ANGLE as system GLES dev option

This change prevents the feature from being inadvertently exposed to the
wider user base while it undergoes further refinement and stabilization
for a smoother user experience.

Test: atest SettingsUnitTests:com.android.settings.development.graphicsdriver.GraphicsDriverEnableAngleAsSystemDriverControllerJUnitTest
Test: locally build Husky and confirm the dev option is disabled, even
with the "debug.graphics.angle.developeroption.enable" prop set.
Flag: EXEMPT bugfix
Bug: b/384047927

Change-Id: I160840a25d38bf305871d7e146745df0d56f0227