refactor: Remove duplicated entries in Directory.Packages.props

[VaclavElias]

Release Type: Latest

Version: n/a

Platform(s): n/a

Describe the bug

Duplicate items in Directory.Packages.props. Not sure if it is on purpose or a bug.

• Microsoft.Direct3D.WARP 2x
• SixLabors.ImageSharp 2x

Additional context
I am getting many warnings about that when building Stride Docs.

[Kryptos-FR]

I'm sure it is not on purpose. It was likely introduced by several PR merges. The entry to keep depends on whether the dependency is used by any runtime project, or only for design (e.g. editor).