add cleanup section to 5.0 upgrade guide

Add cleanup details to upgrade guide as gitolite and more is no longer used.
`sudo -u git -H sh -c 'printf "%b\n%b\n" "PATH=\$PATH:/home/git/bin" "export PATH" >> /home/git/.profile'` from https://github.com/gitlabhq/gitlabhq/blob/4-2-stable/doc/install/installation.md#4-gitolite. My `.profile` was completely differently from the system default at `/etc/skel/.profile` but changes to `.profile` aren't needed after 4.2.