Remove display settings flag checks in DisplayMirroringSwitchTest

The checks of
"com.android.settings.flags.display_topology_pane_in_display_list"
cause test failures.

Bug: 422275864
Test: EnableDisplayMirroringSwitchTest DisableDisplayMirroringSwitchTest
Flag: EXEMPT fixing bug
Change-Id: I1380142cadb3fad807a406ed337865242d05188e