Remove 9 unused search messages

Follows-up r44773 (c4c7d7444948) and r51251 (bbc07fe77605):
* searchmenu-prefix

Follows-up r50207 (abd70a35546b):
* searchmenu-legend

Follows-up r54030 (bde3b1f926a8):
* searchresulttext
* searchsubtitle
* searchsubtitleinvalid
* notitlematches
* nonefound
* powersearch
* powersearch-field

Change-Id: Id5accd7bb66684c9fa3dacb280f7ce9b2920762e
Merge "Remove 9 unused search messages"