Delete branch after merge user preference not being saved on the local storage

Issue Summary

When the user merges a pull request we should store the state of the delete branch after merge checkbox but it is not being saved.

Steps to Reproduce

1. Clean up your browser cache
2. Open a pull request and open the merge dialog
3. You will see the message saying that the checkbox is selected by default
4. Merge the pull request
5. Next pull request you should not see the message anymore

Expected Results

You should not see the message anymore

Actual Results

The message still shows

Workaround

No workaround available