docs(types): remove note of maximum length for raw_text

[zimeg]

Summary

This PR removes the note of a maximum length for raw_text from the table block cell.

Notes

When testing slackapi/python-slack-sdk#1788 it was noticed that 3000+ characters can be contained in a cell, and reference otherwise doesn't indicate a limit:

📚 https://docs.slack.dev/reference/block-kit/blocks/table-block/

Requirements

• I've read and understood the Contributing Guidelines and have done my best effort to follow them.
• I've read and agree to the Code of Conduct.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.02%. Comparing base (8da8e09) to head (e44a0b1).
⚠️ Report is 1 commits behind head on main.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2440   +/-   ##
=======================================
  Coverage   93.02%   93.02%           
=======================================
  Files          40       40           
  Lines       11127    11127           
  Branches      713      713           
=======================================
  Hits        10351    10351           
  Misses        764      764           
  Partials       12       12           

Flag	Coverage Δ
cli-hooks	95.23% <ø> (ø)
cli-test	94.79% <ø> (ø)
oauth	77.39% <ø> (ø)
socket-mode	61.87% <ø> (ø)
web-api	98.08% <ø> (ø)
webhook	96.66% <ø> (ø)

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[zimeg]

@lukegalbraithrussell Your reviews are wonderful. Thank you as always. 🎁 ✨

I'll merge this with remaining thought of how we can map a referenced source of truth to these packages for some future releases...