Group order reset after adding a new group

[aqurilla]

This fixes #10017 by removing the sort that was being carried out after group addition and edit

Mandatory checks

• Change in CHANGELOG.md described in a way that is understandable for the average user (if applicable)
• Tests created for changes (if applicable)
• Manually tested changed features in running JabRef (always required)
• Screenshots added in PR description (for UI changes)
• Checked developer's documentation: Is the information available and up to date? If not, I outlined it in this pull request.
• Checked documentation: Is the information available and up to date? If not, I created an issue at https://github.com/JabRef/user-documentation/issues or, even better, I submitted a pull request to the documentation repository.

[HoussemNasri]

With this PR merged, we're gonna have to reopen JabRef#577. A more sophisticated solution would be to make the sort menu item a check box item, that way when a group is added, we sort subgroups when the sort menu item is checked and keep the same order when it's not.

I think we should merge this PR because it introduces a slightly better behavior (you can sort the groups manually after adding a new group, but you can't go back to the previous order if sorting is done automatically) than the current one until we have a proper solution in place.