Remove remark for subcell limiting support in Trixi2Vtk from docs

[bennibolm]

trixi-framework/Trixi2Vtk.jl#67 was finally merged 🥳 So, the support for subcell data as used in subcell limiting is now in main of Trixi2Vtk.jl.

This PR removes a remark in the Trixi docs.

Mergeable after next Trixi2Vtk release.

[github-actions]

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[bennibolm]

Thanks