Delete manifests/m/Malwarebytes/Malwarebytes/4.6.12.399 directory

[jpdoherty]

The is just a installer file version, not an application version.

Checklist for Pull Requests

• [X] Have you signed the Contributor License Agreement?
• [ ] Is there a linked Issue?

Manifests

• [X] Have you checked that there aren't other open pull requests for the same manifest update/change?
• [X] This PR only modifies one (1) manifest
• [ ] Have you validated your manifest locally with winget validate --manifest <path>?
• [ ] Have you tested your manifest locally with winget install --manifest <path>?
• [ ] Does your manifest conform to the 1.6 schema?

Note: <path> is the name of the directory containing the manifest you're submitting.

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