Rename `*.css.scss` files to `*.scss`

[teoljungberg]

The former seems to be deprecated, according to a stracktrace I found in a Rails app:

DEPRECATION WARNING: Extra .css in SCSS file is unnecessary. Rename vendor/gems/godmin-1.5.0/app/assets/stylesheets/godmin/index.css.scss to vendor/gems/godmin-1.5.0/app/assets/stylesheets/godmin/index.scss. (called from _app_views_welcome_index_html_erb__2091451107232376508_70099202717500 at app/views/welcome/index.html.erb:5)