Removed superfluous TagBar config for golang.

Thanks to 3d430e5c942eac7ea7a7e4d8e548fda1df42d446 which incorporates [fatih/vim-go](https://github.com/fatih/vim-go) (and rightly so!), the prior TagBar global config var that I've removed below should no longer be necessary.

In fact, unless I'm crazy and/or missing something (entirely possible :wink:), [the configurations are exactly the same](https://github.com/fatih/vim-go/blob/master/ftplugin/go/tagbar.vim#L24).

FWIW, I've been using vanilla `fatih/vim-go` + TagBar without the SPF13 `.vimrc` setup and it's been working great.