[APP-1310] Button cleanup (#8754)

* Rm gradient buttons from Storybook

* TEMP move storybook button section

* Remove gradient_sky

* Remove actual defs for gradient_sky and gradient_primary

* Remove other gradient defs

* Remove gradient support entirely

* Deprecate 'variant' in favor of 'color'

* Fork base styles codepath to make variant deprecation more obvious

* Remove text styles for when no color is set, never been used

* Fork text styles codepath to make variant deprecation more obvious

* Revert temp storybook commit, remove deprecated values

* Replace remaining gradient button usage

src/screens/Onboarding/StepProfile/index.tsx

@@ -267,8 +267,8 @@ export function StepProfile() {
         <OnboardingControls.Portal>
           <View style={[a.gap_md, gtMobile && {flexDirection: 'row-reverse'}]}>
             <Button
-              variant="gradient"
-              color="gradient_sky"
+              variant="solid"
+              color="primary"
               size="large"
               label={_(msg`Continue to next step`)}
               onPress={onContinue}>