Remove PCA colormap bug for float output maps

[chungmin99]

Original viewer used to remove both "default" and "pca" colormaps for the float output maps:

nerfstudio/nerfstudio/viewer/server/control_panel.py

Line 364 in 9528a3f

colormap_options = [c for c in list(get_args(Colormaps)) if c not in ("default", "pca")]

However, this is not replicated in the viewer_beta:

nerfstudio/nerfstudio/viewer_beta/control_panel.py

Line 448 in 9528a3f

colormap_options = [c for c in list(get_args(Colormaps)) if c != "default"]

This causes problems when "PCA" is offered as a colormap option (and throws "PCA is not a known colormap" error).

This PR is a one-line change for the bugfix.