Don't link to /android/ urls anywhere, always default to /firefox/

[eviljeff]

Fixes mozilla/addons#16398 (*)

Defaults users to /firefox/ if the app is not specified in the url, and don't link to /android/ anywhere.

Note, the "More..." menu is now a bit pointless, when only one menu item remains, but general UI changes are not in scope for this pr.

(*) the api (in addons-server) is returning urls with /android/ in them, so even though frontend doesn't itself link to /android/, all the search results/shelves still return urls with /android/ in them. mozilla/addons-server#25463 addresses the addons-server changes.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.13%. Comparing base (4f4989c) to head (c67ed67).

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #14469      +/-   ##
==========================================
- Coverage   98.13%   98.13%   -0.01%     
==========================================
  Files         270      270              
  Lines       10751    10702      -49     
  Branches     3315     3296      -19     
==========================================
- Hits        10551    10502      -49     
  Misses        187      187              
  Partials       13       13              

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