Removed unnecessary mutable from GlobalTriggerMenu

The static analyzer was complaining about a mutable in GlobalTriggerMenu.
The mutable keyword was actually unnecessary so was removed.
fix postLS1Customs.py
Merge pull request #4320 from srimanob/fixPostLS1Customs-72X

fix postLS1Customs.py
Merge pull request #4174 from Dr15Jones/removeMutableGlobalTriggerMenu

Removed unnecessary mutable from GlobalTriggerMenu
Merge remote branch 'origin/CMSSW_7_2_X' into CMSSW_7_0_X