TASK: Finally remove removalAttachmentPoint

[mhsdesign]

with soft-removal the removalAttachmentPoint became obsolete but was kept to allow beta-users to upgrade 2b45a2d

See also the issue for a complete history as to what happened.

#4487

TLTR: It was planned to remove this, and we can safely do that now with 9.2 as its non-breaking

Upgrade instructions

Review instructions

Checklist

• Code follows the PSR-2 coding style
• Tests have been created, run and adjusted as needed
• The PR is created against the correct branch:
  • If it's a bugfix, use the lowest maintained branch which has the bug
  • If it's a non-breaking feature, use the branch of the next version (might be either minor or major)
  • If it's a breaking feature it should typically go into the next major version
• Reviewer - PR Title is brief but complete and starts with FEATURE|TASK|BUGFIX
• Reviewer - The first section explains the change briefly for change-logs
• Reviewer - Breaking Changes are marked with !!! and have upgrade-instructions