k2_client: remove more auto-generated cruft

The original k2_client package appeared to have committed a *lot* of
auto-generated stuff into the repo. Remove some more stuff which is
generated for us.
k2_client: delete old manifest.xml file

The manifest.xml file is only used by rosbuild and we don't use
rosbuild.
k2_client: remove more rosbuild cruft

Remove another couple of files, Makefile and mainpage.dox, which are
remnants of the old rosbuild system.
Merge pull request #11 from rjw57/remove-cruft-in-k2-client

Remove cruft in k2 client