Don't do the phrase boost for queries with syntax

Two reasons:
1.  This doesn't normally find anything in its current incarnation.
2.  The phrase rescore tends to require a script score be run across all
matches which can get nasty when the query matches too many things which
is more likely with syntax scores because they can contain things like
<<-foo -bar>> which matches all pages _without_ foo and bar which can
be a ton of pages.

Change-Id: Id12c7516ca71730de3537daa0870ee47aea4cde1