magit-log-edit -> git-commit-mode; "text" snippets -> prog-mode & fundamental-mode

None of the text-mode snippets were actually specific to text-mode;
fixme, todo, and xxx were for making comments, those were moved to
prog-mode. The rest are always useful, those were moved to
fundamental-mode. This allows deleting of many redundant .yas-parents
files which made text-mode a parent of various programming modes.