[fenix] For https://github.com/mozilla-mobile/fenix/issues/23260 - Remove @color/onboarding_card_background_start_gradient_private_theme redirection

app/src/main/res/values/colors.xml

@@ -163,7 +163,6 @@
     <color name="sync_disconnected_icon_fill_private_theme">@color/photonYellow70</color>
     <color name="sync_disconnected_background_private_theme">#5B5846</color>
     <color name="swipe_delete_background_private_theme">@color/photonInk20</color>
-    <color name="onboarding_card_background_start_gradient_private_theme">@color/photonViolet60</color>
     <color name="onboarding_card_background_end_gradient_private_theme">@color/photonPurple50</color>
     <color name="onboarding_illustration_deselected_private_theme">#99FBFBFE</color>
     <color name="prompt_login_edit_text_cursor_color_private_theme">@color/photonViolet50</color>

app/src/main/res/values/styles.xml

@@ -248,7 +248,7 @@
         <item name="syncDisconnected">@color/sync_disconnected_icon_fill_private_theme</item>
         <item name="syncDisconnectedBackground">@color/sync_disconnected_background_private_theme</item>
         <item name="swipeDeleteBackground">@color/swipe_delete_background_private_theme</item>
-        <item name="onboardingDarkGradientStartBackground">@color/onboarding_card_background_start_gradient_private_theme</item>
+        <item name="onboardingDarkGradientStartBackground">@color/photonViolet60</item>
         <item name="onboardingDarkGradientEndBackground">@color/onboarding_card_background_end_gradient_private_theme</item>
         <item name="onboardingSelected">@color/accent_private_theme</item>
         <item name="onboardingDeselected">@color/onboarding_illustration_deselected_private_theme</item>