Fix incorrect instructions in Uninstalling section
In Uninstalling https://tb-manual.torproject.org/uninstalling/ we have instructions that aren't correct.
GitLab is used only for code review, issue tracking and project management. Canonical locations for source code are still https://gitweb.torproject.org/ https://git.torproject.org/ and git-rw.torproject.org.
In Uninstalling https://tb-manual.torproject.org/uninstalling/ we have instructions that aren't correct.