Remove 'Higher speech rate' button based on the results of the speech
rate slider a11y UX study.

Also, group speech rate, sample sentence synthesis and default language
status into a single preference category as they all fall under the
general TTS settings category.

Bug: 24527715
Change-Id: If7253e2e8a468393afcb4c24f5a775cb9af79db9
2 files changed