Remove direct qtaguid access from platform/system apps

System components should use the public tagSocket() API, not direct
file access to /proc/net/xt_qtaguid/* and /dev/xt_qtaguid.

Test: build/boot taimen-userdebug. Use youtube, browse chrome,
    navigate maps on both cellular and wifi.
Bug: 68774956

Change-Id: Id895395de100d8f9a09886aceb0d6061fef832ef