Remove skeleton

[skade]

Kills the last 2 mentions of skeleton classes, removes the CSS file.

I went through all pages, but please do so again on review.

[pietroalbini]

Can someone else review this? I'm pretty filled with other stuff right now.

[Mark-Simulacrum]

A quick grep for skeleton finds some button-secondary--no-skeleton classes and such in the code which should probably be removed along with skeleton in this PR:

templates/learn/index.hbs
50:{{!-- TODO: Remove button-secondary--no-skeleton once Skeleton is completely removed. --}}
55:             class="button button-secondary button-secondary--no-skeleton mw6-l w-100">{{text learn-doc-std-button}}</a>
63:             class="button button-secondary button-secondary--no-skeleton mw6-l w-100">{{text learn-doc-edition-button}}</a>
71:             class="button button-secondary button-secondary--no-skeleton mw6-l w-100">{{text learn-doc-cargo-button}}</a>
79:             class="button button-secondary button-secondary--no-skeleton mw6-l w-100">{{text learn-doc-rustdoc-button}}</a>
87:             class="button button-secondary button-secondary--no-skeleton mw6-l w-100">{{text learn-doc-rustc-button}}</a>
95:             class="button button-secondary button-secondary--no-skeleton mw6-l w-100">{{text learn-doc-error-button}}</a>
108:               class="button button-secondary button-secondary--no-skeleton mw6-l w-100">
118:               class="button button-secondary button-secondary--no-skeleton mw6-l w-100">
128:               class="button button-secondary button-secondary--no-skeleton mw6-l w-100">

src/styles/app.scss
113:.button.button-secondary--no-skeleton {

[skade]

@Mark-Simulacrum right, thank you

[skade]

@Mark-Simulacrum It's been a while. Updated.

[Mark-Simulacrum]

r=me with Skeleton removed from CONTRIBUTING.md as well

[skade]

Removed from contributing, merging when checks are green.