No description is better than one that refers to removed code
Remove custom themes and simply provide a custom style for all

This is what the themes were effectively doing.
Replace massive overlays by simply removing Commenting from the UI

Removes Comment from the Actions menu, "private" from available
UpdateTypes, and the per-transaction "Comment" links.

RT::Ticket->Comment is already overridden to forbid comments at the API
level.
Preserve inc/.author across git clean