Removed unnecessary mutables from FP420 cluster classes

[Dr15Jones]

These unneeded mutables were causing the static analyzer to complain.
Removing them caused no other changes to the code.

[cmsbuild]

A new Pull Request was created by @Dr15Jones (Chris Jones) for CMSSW_7_1_X.

Removed unnecessary mutables from FP420 cluster classes

It involves the following packages:

DataFormats/FP420Cluster

@nclopezo, @cmsbuild, @anton-a, @thspeer, @slava77, @Degano can you please review it and eventually sign? Thanks.
You can sign-off by replying to this message having '+1' in the first line of your reply.
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@nclopezo, @ktf you are the release manager for this.
You can merge this pull request by typing 'merge' in the first line of your comment.

[cmsbuild]

+1
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-3437/976/summary.html

[cmsbuild]

Comparison is ready
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-3437/976/summary.html

[slava77]

+1

for #3437 5ecb374
tested in CMSSW_7_1_X_2014-04-23-0200
(test area sign352)
no regressions observed on short matrix tests

[cmsbuild]

This pull request is fully signed and it will be integrated in one of the next CMSSW_7_1_X IBs unless changes (tests are also fine). @nclopezo, @ktf can you please take care of it?