prepare to delete METProducer

In https://github.com/cms-sw/cmssw/pull/1745, six dedicated new producers to replace METProducer were merged. 

In https://github.com/cms-sw/cmssw/pull/1936, HLT configuration started using CaloMETProducer, one of the new  dedicated producers, instead of METProducer.

This pull request replace further remaining METProducer with new dedicated producers.

After this request is merged, I think then we can actually delete METProducer.