Remove NERDCommenter config

Nobody uses it, right?
Remove set modelines=5

This is already the default.
Remove t_Co override

The conditional was broken (should have been using =~, not ==), and it's
now in sensible.vim anyways.
Kill <F1> map

I'm pretty sure this was added exclusively to service my fat fingers.
Bring it back if you miss it.
Kill syntax/filetype on in hashrocket.vim

This is already in .vimrc.