Thread safety cleanup in SiStripRecHitMatcher

Modify return type of SiStripRecHitMatcher::match
from a bare pointer to a unique_ptr. This eliminates
a report from the thread safety static code checker
of a potential thread safety problem. Also modify the
one file where this function is called to use
the new interface.
Merge pull request #3517 from wddgit/threadSafetySiStripRecHitMatcher2

Multithreading -- Thread safety cleanup in SiStripRecHitMatcher