remove trac documentation now that it is retired

howto/trac.md

-Important note: Trac was migrated to [howto/GitLab](howto/GitLab) in June 2020. See
-[howto/gitlab](howto/gitlab#Migration) for the details. This is kept only for historical
-reference.
-
-Commandline access
-==================
-
-We use [cartman](https://github.com/tamentis/cartman/), a "commandline trac client" which "allows you to
-create and manage your Trac tickets from the command-line, without the
-need to setup physical access to the Trac installation/database".
-
-Install:
-
-    virtualenv --python=python3 --system-site-packages ~/.virtualenvs/cartman
-    ~/.virtualenvs/cartman/bin/pip install cartman
-    alias cm=~/.virtualenvs/cartman/bin/cm
-
-Config:
-
-    [trac]
-    base_url = https://trac.torproject.org/projects/tor
-    username = anarcat
-    password = ....
-    auth_type = basic
-
-The password can be ommitted and passed through the environment
-instead with [this patch](https://github.com/tamentis/cartman/pull/30).
-
-Template:
-
-    To: anarcat
-    Cc: 
-    Milestone: 
-    Component: Internal Services/Tor Sysadmin Team
-    Priority: Medium
-    Type: defect
-    Keywords: 
-    Version: 
-    Subject: test
-
-    test
-
-Running:
-
-    TRAC_PASSWORD=$(pass trac.torproject.org) cm new
-
-Other documentation
-===================
-
-There's very little documentation on our Trac instance out there. This
-page was originally created to quickly jot down notes on how to
-batch-create tickets. There's also a [Trac page in the Tor Trac
-wiki](https://gitlab.torproject.org/legacy/trac/-/wikis/org/operations/services/trac) and the [upstream documentation](https://trac.edgewall.org/).