fix(email-first): Fix FxA resizing in the firstrun page for email-first (#5765); r=rfk
fix(email-first): Fix FxA resizing in the firstrun page for email-first (#5765); r=rfk

The min-height forced the iframe to be too large on the firstrun page
in the email-first flow. In chromeless, it doesn't really matter
how big the #main-content is, there's no shadow, etc, to display.

Remove the min-height: 300 declaration for chromeless
mozilla/fxa-content-server,mozilla/fxa-content-server,shane-tomlinson/fxa-content-server,mozilla/fxa-content-server,shane-tomlinson/fxa-content-server,shane-tomlinson/fxa-content-server