On pressing backspace+Enter, keep cursor indent
Remove special comment handling

Comments seem to be handled fine without it, except their behaviour
matches the new backspacing behaviour -- when the user backspaces after
a comment line, their indentation is preserved when they hit "Enter".
set nosmartindent

Smart indent seems to be useful for C, but not necessary in this case.
Handle comments

In the end, there has to be an explicit check for comments, or they get
indented just like normal code.