GitLab: drop one obsolete reference to Salsa

wiki/src/contribute/APT_repository/custom.mdwn

@@ -435,6 +435,6 @@ Contributing without privileged access
 
 Non-core developers without access to the "private" APT infrastructure
 would add the .deb they want to their Git branch as we have been
-doing until now, push the result to Salsa or whatever... and at
+doing until now, push the result to their own Git repository... and at
 merge time, we would rewrite their history to remove the .deb, and
 import it into our APT repo.