Get rid of `warning: refs/remotes/origin/master usually tracks refs/heads/master, not refs/remotes/origin/master`

Hello Git,

Found this issue and could find a solution.

Repro steps:

1. create a simple repo with only the master branch.
2. `git pull origin *:*` to allocate all refs (no warnings)

If try to mirror the repo into the same remote:

1. `git push origin --mirror`

Then the remote counter part falls into the mirror state and reports the warning:

1. `git pull origin *:*`

``` warning: refs/remotes/origin/master usually tracks refs/heads/master, not refs/remotes/origin/master Already up to date. ```

Tried to delete all refs in the local and remote. But didn't work. Somehow the remove remember the state.

Is there a way to unmirror the remote repository back?