Dedupe last used tags

[Pytal]

Summary

array_unique returns a new array rather than mutating the original array in-place

Before	After
["5","2","4","4","3","3","2","2","1","1"]	["5","2","4","3","1"]

Technically the array will not be made unique until the next time the user selects a tag but it’s probably not worth adding a background job for this as the existing frontend code still sorts the tags correctly

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)