Cleanup removed files from RuboCop TODOs and rspec_order_todo.yml

What does this MR do and why?

This commit removes excludes from RuboCop TODOs and rspec_order_todo.yml for removed/non-existent files.

Done via https://gitlab.com/-/snippets/2482940.

Follow-up of !105695 (comment 1235132373).

Supersedes !108665 (merged).

How to set up and validate locally

# Check diff
git diff HEAD~

# Collect files removed
git diff HEAD~ | rg -r '$1' -o '^-\s+- (\S+)' | sort | uniq

# Check if they still exist via `stat`
git diff HEAD~ | rg -r '$1' -o '^-\s+- (\S+)'  | sort | uniq | xargs stat -c "%n" {} 2>/dev/null
# No output

# Verify by touching a removed file like `spec/models/issue_collection_spec.rb`
touch spec/models/issue_collection_spec.rb

# Run again
git diff HEAD~ | rg -r '$1' -o '^-\s+- (\S+)'  | sort | uniq | xargs stat -c "%n" {} 2>/dev/null
spec/models/issue_collection_spec.rb

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.