Refactor eliminate required email

@seanmonstar, @6a68, anybody else that wants to review. I don't mind. I want the remnants of this PITA feature out of the code. 907 total LOC removed. 

An ephemeral instance, https://no-required-email.personatest.org is available to test.

Note, no Selenium tests were changed in this PR, so I am somewhat confident that user facing functionality is the same. I did change a couple of selectors, which will require me to notify @stephend and co.

fixes #1873