Using execCommand to replace the entire contents of the textarea is very slow for larger posts (it seems the browser does a reflow after every 'virtual keypress').
This commit updates the `maybeContinueList()` function to be more surgical when removing the bullet. Now it only selects & removes the characters which actually need to be deleted
Similar to a7cd2207048bfac3e76fafdf47e259cd1b391352