refactor some links in howto/ldap

howto/ldap.md

@@ -1033,13 +1033,15 @@ starts with the `!` string).
 ### Web interface
 
 The web interface is shipped as part of the userdir-ldap-cgi Debian
-package, built from the [userdir-ldap-cgi source code](https://gitweb.torproject.org/admin/userdir-ldap-cgi.git/). The web
+package, built from the [userdir-ldap-cgi repository][]. The web
 interface is written in Perl, using the builtin CGI module and [WML][]
 templates. It handles password and settings changes for users,
 although some settings (like sudo passwords) require an extra
 confirmation by OpenPGP-signed message through the email gateway. It
 also lists machines known by LDAP.
 
+[userdir-ldap-cgi repository]: https://gitweb.torproject.org/admin/userdir-ldap-cgi.git/
+
 The web interface also ships documentation in the form of HTML pages
 rendered through [WML][] templates.
 
@@ -1345,8 +1347,8 @@ Bacula.
 
 ## Other documentation
 
- * our (TPA) [userdir-ldap source code](https://gitweb.torproject.org/admin/userdir-ldap.git/)
- * our (TPA) [userdir-ldap-cgi source code](https://gitweb.torproject.org/admin/userdir-ldap-cgi.git/)
+ * our (TPA) [userdir-ldap repository][]
+ * our (TPA) [userdir-ldap-cgi repository][]
  * the [DSA wiki](https://dsa.debian.org/) has some ud-ldap documentation, see in
    particular:
    * [how to get sudo passwords](https://dsa.debian.org/user/sudo/)
@@ -1370,13 +1372,16 @@ Bacula.
 it could be older) and is hard to debug and extend. This section aims
 at documenting issues with the software and possible alternatives.
 
-Our [userdir-ldap repository](https://gitweb.torproject.org/admin/userdir-ldap.git/) is a fork of the [DSA userdir-ldap
-repository](https://salsa.debian.org/dsa-team/mirror/userdir-ldap). The codebase is therefore shared with the Debian
+Our [userdir-ldap repository][] is a fork of the [DSA userdir-ldap
+repository][]. The codebase is therefore shared with the Debian
 project, which uses it more heavily than TPO. According to [GitLab's
 analysis](https://salsa.debian.org/dsa-team/mirror/userdir-ldap/-/graphs/master), weasel has contributed the most to the repository (since
 2007), followed closely by Joey Schulze, which wrote most of the code
 before that, between 1999 and 2007.
 
+[DSA userdir-ldap repository]: https://salsa.debian.org/dsa-team/mirror/userdir-ldap
+[userdir-ldap repository]: https://gitweb.torproject.org/admin/userdir-ldap.git/
+
 The service is mostly in maintenance mode, both at DSA and in TPO,
 with small, incremental changes being made to the codebase over all
 those years. Attempts have been made to rewrite it with a Django