Remove SCSS rules for "#body-login" elements

"#body-login" is only used in the layout for guest pages. Therefore,
before SCSS was enabled for guest pages, all "#body-login" rules in SCSS
files were ignored. Now that SCSS is enabled for guest pages those rules
break the guest pages, but given that they were ignored until now they
can be safely removed.

Note, however, that all of the above refers to regular SCSS rules; those
defined in the Theming app are different, as they were converted to CSS
and used in the guest pages even when SCSS was disabled, so they do not
need to be adjusted due to SCSS being enabled now.

Signed-off-by: Daniel Calviño Sánchez <danxuliu@gmail.com>