Stop making PreferenceFragment fit system windows

A PreferenceFragment might not fill its window. Setting
android:fitsSystemWindows="true" might cause redundant padding if the
fragment is away from the WindowInsets.

Instead, the app which uses PreferenceFragment should handle insets.

This CL partially reverts commit:
213033ec

Bug: 377864165
Bug: 309578419
Flag: com.android.window.flags.enforce_edge_to_edge
Test: atest CtsPreferenceTestCases
Change-Id: Ic55f0e3c6264982c0ba5aeffba20f26ddf9052ee