Fix thread safety issues by removing mutable data members of MuonDetIdAssociator 

The class MuonDetIdAssociator contained two mutable data members, both vectors, that were modified by const member functions of the class.  This is not thread safe.
This pull request removes the mutable data members.  Instead, a vector is passed in to the functions for filling by the functions.  There is no need to store the vectors in the class.
Tested with checkdeps -a and the relval matrix.