[Flag cleanup] remove separate_accessibility_vibration_settings_fragments

This bug fix associated with this flag is low risk. The flag has been
soaked in the Trunkfood full for 30 days and tested by 1000+ users.
Based on the flag cleanup policy, we can clean up the flag.

Bug: 289967175
Flag: EXEMPT flag cleanup
Test: Run the Settings app and can still see the vibration & haptics
screen

Change-Id: I39890a33f04b53565461ae2c6c4e63b94f205e6d