irc.utils: remove deprecated CapReq.module property

[dgw]

Description

Tin. We've reached the documented removed_in point for this obsolete prop.

Another thing that's not listed at #1738 but is still technically part of that initiative.

Checklist

• I have read CONTRIBUTING.md
• I can and do license this contribution under the EFLv2
• No issues are reported by make qa (runs make quality and make test)
  • Again, no test code references this, so I'm leaning on CI to run that against 4 Python versions faster than I can run it against even just one.
• I have tested the functionality of the things this change touches