Login and Registration: Hide the login form on the "check your email" step of...

Login and Registration: Hide the login form on the "check your email" step of new user registration or password reset.

This aims to reduce some confusion and make it clearer that the email should be checked before attempting to log in right away.

Props rianrietveld, pratik028, bdbch, johnbillion, hankthetank, yashrs, williampatton, audrasjb, bmartinent, florianatwhodunit, henry.wright, birgire, SergeyBiryukov.
Fixes #40605, #41514.
Built from https://develop.svn.wordpress.org/trunk@48304


git-svn-id: https://core.svn.wordpress.org/trunk@48073 1a063a9b-81f0-0310-95a4-ce76da25c4cd