Remove gh-pages branch on kobuki_core repo.

[Younghun Ju]

Unnecessary and duplicated.

[Marcus Liebhardt]

Actually this information (http://yujinrobot.github.io/kobuki/) belongs to kobuki_core, but on the other hand the url http://yujinrobot.github.io/kobuki/ is nicer. So 👍

[Daniel Stonier]

I agree. Serving the doxygen pages from github.com/yujinrobot/kobuki/gh-pages is nicer, and avoids linking errors if we change it.

As young hoon said though, that does mean gh-pages on kobuki_core is duplicated.

Thanks for volunteering to do the job young hoon ;)

[Younghun Ju]

Ouya, removed!