[vim] Add mm and remove h from objc syntax
[vim] Add mm and remove h from objc syntax

I don't touch objc headers nearly as much so this was too aggressive.
I'm not sure if mm should really be objc, but I guess that normally
implies it's more objc than C++

keith/dotfiles,keith/dotfiles,keith/dotfiles,keith/dotfiles,keith/dotfiles,keith/dotfiles