Remove improper call to edm::Ref constructor call

[Dr15Jones]

The associator was constructing an edm::Ref by passing it an
edm::RefVector and an index. However, the index used was one into
the edm::RefVector but the constructor requires the index to be back
to the original collection to which the edm::RefVector associates.
The only way the associator ever worked correctly was when the edm::RefVector
used contained entries for every item in the original collection.
The problematic edm::Ref constructor will be removed in another commit.
This problem was found by David Dagenhart.

[cmsbuild]

A new Pull Request was created by @Dr15Jones (Chris Jones) for CMSSW_7_4_X.

Remove improper call to edm::Ref constructor call

It involves the following packages:

SimMuon/MCTruth
SimTracker/TrackAssociation
SimTracker/TrackAssociatorProducers

The following packages do not have a category, yet:

SimTracker/TrackAssociatorProducers

@cmsbuild, @civanch, @nclopezo, @mdhildreth can you please review it and eventually sign? Thanks.
@battibass, @makortel, @threus, @abbiendi, @GiacomoSguazzoni, @rovere, @VinInn, @appeltel, @cerati, @trocino, @dgulhan, @venturia this is something you requested to watch as well.
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[Dr15Jones]

please test

[cmsbuild]

The tests are being triggered in jenkins.

[cmsbuild]

+1
Tested at: 4c59972
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-7463/2234/summary.html

[cmsbuild]

Comparison is ready
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-7463/2234/summary.html

[civanch]

+1

[davidlange6]

@Degano - could you please assign SimTracker/TrackAssociatorProducers to SIM category.
Thanks