Remove ANGLE from base_system.mk

Removing GoogleANGLE only removed the Google-signed version of ANGLE,
but the AOSP version still remained. This CL removes the AOSP build of
ANGLE also, so there is no ANGLE on the device at all.

Bug: 158956138
Test: adb shell pm list packages | grep -i angle
Change-Id: If9a42bc6436c752d2b1a16565d99ca2a5ec60d66