commands/command_migrate.go: use formatRefName to qualify references
commands/command_migrate.go: use formatRefName to qualify references

Per our work in the previous commit(s), it is now suitable to call
formatRefName() again thus avoiding our "hack" to prepend the remote
name to the reference before calling '(*git.Ref) Refspec()'.

As such, let's do that.

Co-authored-by: brian m. carlson <4444590e73774f57a657cae774d430e75550d837@github.com>

github/git-lfs,github/git-lfs,github/git-lfs