Revert "Add support for ASGI pathsend extension"

[gi0baro]

This reverts #2435.
Superseed #2616, as discussed in comments.

Checklist

• I understand that this PR may be closed in case there was no previous discussion. (This doesn't apply to typos!)
• I've added a test for each change that was introduced, and I tried as much as possible to make a single atomic change.
• I've updated the documentation accordingly.

[Kludex]

@gi0baro I made the 0.38.1 release with this change.