Removed old Timing plugin declaration

In the recent change that added a base class to the Timing Service, the old plugin declaration was not removed. This caused two plugin declarations for the same Service to appear and confuses the PluginManager when attempting to load the requested Service.
Merge pull request #4250 from Dr15Jones/removeOldTimingPluginDeclaration

Removed old Timing plugin declaration
Merge remote branch 'origin/CMSSW_7_2_X' into CMSSW_7_0_X