Future of snippet search

Problem to solve

Discovered while working on: !123668 (merged)

Snippet search is not fully functional (reported by @maddievn) and has some usability issues:

• difficult to find. tabs do not show up by default. you must be in a specific context to search (searching from https://gitlab.com/dashboard/snippets is one way)
• web UI does not use scope param like all other scopes (API does respect the scope param). It uses snippets=true
• not listed in documentation as supported by Advanced Search
• counts are duplicated across all scopes
• once in snippets search, the clicking any other tab does not switch the scope, probably due to the use of snippets=true param

Proposal

I propose to remove snippet search from the web UI interface and consider removing from API (though this would be a breaking API change and not sure that is possible).