removed all email signups ab test code (hopefully)
Merge pull request #2865 from guardian/revert-email-signups

Remove all email signups AB test code
Merge branch 'master' of https://github.com/guardian/frontend into revert-chartbeat-and-commercial-tests

Conflicts:
	common/app/assets/javascripts/modules/experiments/ab.js
	common/app/conf/switches.scala