* "mail/issue/default.tmpl": the body is rendered by backend
`markdown.RenderString() HTML`, it has been already sanitized
* "repo/settings/webhook/base_list.tmpl": "Description" is prepared by
backend `ctx.Tr`, it doesn't need to be sanitized
This PR cleans up the docs in a way to make them simpler to ingest by
our [docs repo](https://gitea.com/gitea/gitea-docusaurus).
1. It includes all of the sed invocations our ingestion did, removing
the need to do it at build time.
2. It replaces the shortcode variable replacement method with
`@variable@` style, simply for easier sed invocations when required.
3. It removes unused files and moves the docs up a level as cleanup.
---------
Signed-off-by: jolheiser <john.olheiser@gmail.com>
