shell-app: Remove MATCH_MULTIPLE_{PREFIX,SUFFIX}

We originally OR'ed search terms and favored results which matched
multiple times to get more relevant results. When changing search
to AND search terms, the semantics of "multiple matches" were
changed to refer to a single term matching multiple criteria (name,
executable), which seemed like a good idea at the time.

However in practice this just results in applications whose
user-visible name matches the executable name on disk being
favored over applications using a more generic name, which
isn't too useful (in particular when taking usage frequency
into account).

https://bugzilla.gnome.org/show_bug.cgi?id=623372