Update Deny-Private-DNS-Zones.json

[theomper]

Overview/Summary

This PR removes an unnecessary square bracket '[' in the json file definition of policy "Deny-Private-DNS-Zone"

This PR fixes

1. Syntax error in file Deny-Private-DNS-Zone.json

As part of this Pull Request I have

• [ ] Checked for duplicate Pull Requests
• [ ] Associated it with relevant issues, for tracking and closure.
• [ ] Ensured my code/branch is up-to-date with the latest changes in the main branch
• [ X ] Performed testing and provided evidence.
• [ ] Ensured contribution guidance is followed.
• [ ] Updated relevant and associated documentation.
• [ ] Updated the "What's New?" wiki page (located: /docs/wiki/whats-new.md)

[Springstone]

@theomper it looks like you're removing a mandatory extra [, which is needed in this repo as we automatically generate a payload that requires this "escape" character. You cannot deploy policies in this repository as is, if you copy the definition you will need to remove the leading [ before using it in Azure directly. If this is the issue you we're trying to fix, please close the PR.