[Halld-offline] change to DTrackCandidate_factory_CDC

[Simon Taylor]

Hi.
I've made a change in DTrackCandidate_factory_CDC with regard to how FDC 
hits are handled.  The previous version of the code tried to use
FDC hits to improve the track candidates if the code determined that 
there might be insufficient hits in the cdc to get a good candidate.    
In the absence of noise hits, this functionality is now redundant with 
the latest version of the main DTrackCandidate factory and so I have 
removed the matching to FDC hits from the CDC track candidate factory.   
If there are noise hits in the FDC, the previous version could have lead 
to erroneous matches between stray hits in the  FDC not associated with 
segments and CDC track candidates.   However, if these hits should have 
been associated with the CDC hits, they are in principle recovered 
during the hit selection stage.

Simon