Remove VibrationAttributes#CATEGORY_KEYBOARD (in Settings)

Since CL[1], [2] introduced USAGE_IME_FEEDBACK in VibrationAttributes
to be able to specify default / current vibration in VibrationSettings
according to the vibration usage naturally without using this category
attribute + a bypass flag to only support a fixed vibration scaling.

Remove CATEGORY_KEYBOARD attribute and replacing with USAGE_IME_FEEDBACK
in Settings for cleaning up logic.

[1]: I6256c4f47a8bbee4b649d35eabfbc0c94215c0d7
[2]: I764aa8bd72889d4af62b30bff75af9033f22052b

Flag: EXEMPT refactor
Bug: 332661766
Test: atest KeyboardVibrationTogglePreferenceControllerTest
Change-Id: I532e7d184d235bfa266fb590e60802c4e2fa7df2