Revert "Made mutable in EventSetupRecord atomic"

This reverts commit 64bd0d4464b3fdbf99ee884e382f58c555ad45ae.
Merge pull request #3521 from ktf/revert-3504

Revert "Made mutable in EventSetupRecord atomic"
Merge remote branch 'origin/CMSSW_7_1_X' into CMSSW_7_0_X