Delete .gitmodules

It doesn't seem like we need this submodule anymore since the script clones vundle itself.

is there a reason it's still here?
Screen program mapping is now opt-in
This as it slows down exit from insert mode for many users
Removed screen program mapping
Merge pull request #559 from rekendahl/3.0

Screen program mapping is now opt-in (as it slows down exits from insert back to normal mode)
Merge pull request #556 from jrobeson/patch-1

Delete .gitmodules