Hide running time for "Android System" in the optimization page

Hide the running time information for "Android System" entry, since this
entry will combine multiple system components together. It will provide
incorrect running time information. The getRealUid() method maps many
UIDs to Process.SYSTEM_UID(1000), which results in combining all of
those UIDs into one "Android System" entry. This is the expected behavior.

Bug: 220717612
Test: make RunSettingsRoboTests -j56 ROBOTEST_FILTER="com.android.settings.fuelgauge"
Change-Id: I9d44fe8490ad5c684419b8ebf8d7d5576a42788a