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

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

@@ -166,7 +166,6 @@
     <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="add_on_private_browsing_exterior_circle_background_private_theme">@color/accent_private_theme</color>
     <color name="prompt_login_edit_text_cursor_color_private_theme">@color/photonViolet50</color>
 
     <!-- Tab Tray -->

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

@@ -252,7 +252,7 @@
         <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>
-        <item name="addOnPrivateBrowsingExteriorCircleBackground">@color/add_on_private_browsing_exterior_circle_background_private_theme</item>
+        <item name="addOnPrivateBrowsingExteriorCircleBackground">@color/accent_private_theme</item>
         <item name="addOnPrivateBrowsingInteriorIconBackground">@color/photonWhite</item>
         <item name="mozacPromptLoginEditTextCursorColor">@color/prompt_login_edit_text_cursor_color_private_theme</item>
         <item name="awesomeBarIndicatorColor">@color/photonGreen60</item>