mwgrep: do not quote search term

Follows Ie8bf4cdc3. The quotes are interpreted as part of the search term. This
was a bug before too, but the fact that I wasn't using the keyword analyzer
obscured it.

Change-Id: Ib3f0ff21e02abe68eef68e123a555f2d7b5b1aac
Merge "mwgrep: do not quote search term" into production