harmonize migration heading with others

The "how to" bit is redundant. We keep an anchor for backwards
compatibility.

howto/git.md

@@ -240,7 +240,8 @@ Changes to most repositories are reported to:
 
  * Some repositories have a dedicated mailing list for commits at https://lists.torproject.org
 
-## How to migrate a Git repository from legacy to GitLab?
+<a id="how-to-migrate-a-git-repository-from-legacy-to-gitlab"></a>
+## Migrating a repository to GitLab
 
 Moving a repository from Gitolite to GitLab proceeds in two parts. One
 part can be done by any user with access to GitLab. The second part