Enable free color/species input on ItemPage

Previously, I kept this constrained to valid species/color pairs only, because we didn't have a great error state. But at this point, it feels worse to throw people out of the color they're looking at, and to make it harder for them to pick the color in the first place!

src/app/ItemPage.js

@@ -690,11 +690,6 @@ function ItemPageOutfitPreview({ itemId }) {
             speciesIsDisabled={isProbablySpeciesSpecific}
             size="sm"
             showPlaceholders
-            // This is just a UX affordance: while we could handle invalid states
-            // from a UI perspective, we figure that, if a pet preview is already
-            // visible and responsive to changes, it feels better to treat the
-            // changes as atomic and always-valid.
-            stateMustAlwaysBeValid
           />
           <Box flex="1 0 0" lineHeight="1">
             {isIncompatible && (