fix: Remove explicit bg color from active filter buttons

[choo121600]

In light mode, the active button was rendered with colorPalette.muted, causing the button color to appear washed out.

Since the solid variant already provides sufficient visual distinction for the active state,
the additional muted background override has been removed.

I had only been looking at dark mode, but once I checked light mode, the issue became noticeable 😅

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After

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[choo121600]

This change is already included in PR #60346, so I’ll close this one.