chore: revert tsconfig changes for local development

[SychO9]

Changes proposed in this pull request:
Changes here 4e52f0e have yielded unwanted effects in that dist typings also complied core and extension sources in other extensions.

Attempted to fix that through changing action build to allow deleting unwanted files, but got even more problems, so reverting fo now.

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.