Remove haml duplicates from Snippet/Show

What does this MR do?

Removes unused references to haml files in Dashboard/Snippet/Show. Now that :snippet_vue feature flag is enabled by default, only vue components are visible to users (and automation). See https://gitlab.com/gitlab-org/quality/team-tasks/-/issues/492#note_335592893

Also, several elements renamed to comply with our Element naming convention.

Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry
• [-] Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [-] Database guides
• [-] Separation of EE specific content