Remove arch-specific tags from .NET Aspire Dashboard

[lbussell]

See Announcement: New tagging scheme for .NET Monitor, Aspire Dashboard, and samples (#5961) and Undocument arch-specific tags on .NET appliance images (#5946) for context.

This issue tracks removing the arch-specific tags for .NET Aspire Dashboard images in the .NET Aspire 9.0 release timeframe.

[lbussell]

[Triage] @joperezr can you make sure to include this change for Aspire Dashboard 9.0 images?

[lbussell]

These were undocumented in #5955. Removal is blocked on feature work in ImageBuilder.