feat(tags): remove unused tags APIs

[gary02]

remove below unused APIs and related resolvers:

• User.maintainedTag
• User.pinnedTags
• Tags.isPinned
• togglePinTag

resolve https://github.com/thematters/developer-resource/issues/440

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 58.74%. Comparing base (fd2237b) to head (08444f2). Report is 1 commits behind head on develop.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## develop #4000 +/- ## =========================================== + Coverage 58.69% 58.74% +0.05% =========================================== Files 890 886 -4 Lines 17224 17178 -46 Branches 3077 3071 -6 =========================================== - Hits 10109 10091 -18 + Misses 7064 7036 -28 Partials 51 51 ```

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