Fixes #0000

Changes proposed in this pull request:

• Removes unused imports which were caught by temporarily adding "noUnusedLocals": true to the global flarum-tsconfig and running tsc --noEmit --emitDeclarationOnly false.

Reviewers should focus on:
It may be worth thinking about if "noUnusedLocals": true and/or "noUnusedParameters": false should become part of the official flarum-tsconfig or perhaps if that should just be used in the framework itself, without imposing it to everyone extending the baseline config. Thoughts on that?

Screenshot

Necessity

• Has the problem that is being solved here been clearly explained?
• If applicable, have various options for solving this problem been considered?
• For core PRs, does this need to be in core, or could it be in an extension?
• Are we willing to maintain this for years / potentially forever?

Confirmed

• Frontend changes: tested on a local Flarum installation.
• Backend changes: tests are green (run composer test).
• Core developer confirmed locally this works as intended.
• Tests have been added, or are not appropriate here.

Required changes:

• Related documentation PR: (Remove if irrelevant)