Remove scss variables, part 2
Removes:
$gl-text-green
$gl-text-green-hover
$gl-text-red
$placeholder-text-color
$gl-link-color
$gl-text-orange
$gl-link-hover-color
$gl-gray
$gl-header-nav-hover-color
Related to https://gitlab.com/gitlab-org/gitlab-ce/issues/49807
Edited by Annabel Dunstone Gray