Rework UI labels for Bulk Edit Phoneme Features

From LT-10432:
1. Remove use of the Phonological feature chooser (for now; may return to
   this if users ask for a way to set multiple features at once).
2. Call the view "Bulk Edit Phoneme Features"
3. Use "Phoneme" instead of "Refer to as"
4. Change "Remove this feature" to "Blank"
5. Label the Target dropdown box as "Choose Feature:"
6. Label the Change To: dropdown box as "Choose Value:"
7. Make the Bulk Edit Operation explanation text read:
   Select a feature and a value to change it to
8. Label the one and only tab as "List Choice"

Change-Id: I871c5698326ca4764fb6b1013c14b5b34b4c639b