[fenix] For https://github.com/mozilla-mobile/fenix/issues/23319 - Replace mozac_widget_favicon_background_color to @color/fx_mobile_layer_color_2

@color/mozac_widget_favicon_background_normal_theme and @color/fx_mobile_layer_color_2 are equivalent

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

@@ -130,7 +130,6 @@
     <color name="search_suggestion_indicator_icon_bookmark_color_normal_theme">@color/photonBlue40</color>
     <color name="recently_used_share_theme">@color/photonDarkGrey10</color>
 
-    <color name="mozac_widget_favicon_background_normal_theme">@color/photonDarkGrey50</color>
     <color name="mozac_widget_favicon_border_normal_theme">@color/photonDarkGrey10</color>
 
     <!-- Tab tray -->

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

@@ -196,7 +196,6 @@
     <color name="prompt_login_edit_text_cursor_color_normal_theme">@color/photonInk20</color>
     <color name="search_suggestion_indicator_icon_color_normal_theme">@color/photonGreen70</color>
     <color name="search_suggestion_indicator_icon_bookmark_color_normal_theme">@color/photonBlue50</color>
-    <color name="mozac_widget_favicon_background_normal_theme">@color/photonWhite</color>
     <color name="mozac_widget_favicon_border_normal_theme">@color/photonLightGrey30</color>
     <color name="recently_used_share_theme">@color/photonLightGrey30</color>
 

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

@@ -87,7 +87,7 @@
         <!-- Shared widget colors -->
         <item name="mozac_primary_text_color">@color/primary_text_normal_theme</item>
         <item name="mozac_caption_text_color">@color/caption_text_normal_theme</item>
-        <item name="mozac_widget_favicon_background_color">@color/mozac_widget_favicon_background_normal_theme</item>
+        <item name="mozac_widget_favicon_background_color">@color/fx_mobile_layer_color_2</item>
         <item name="mozac_widget_favicon_border_color">@color/mozac_widget_favicon_border_normal_theme</item>
 
         <item name="tabTrayItemMediaBackground">@color/accent_normal_theme</item>