MC-31168: [2.3.x] Mark core payment methods as deprecated in Admin

Author: svitja

app/design/adminhtml/Magento/backend/Magento_Config/web/css/source/_module.less

@@ -150,10 +150,10 @@
 }
 
 .deprecated-message > .comment {
-    background: #faecec;
-    border: 1px solid #d6474a;
+    background: @deprecated__light_color;
+    border: 1px solid @deprecated__dark_color;
     border-radius: 3px;
-    color: #d6474a;
+    color: @deprecated__dark_color;
     margin: 5px 0 0;
     padding: 3px 7px;
     position: relative;

lib/web/css/source/lib/variables/_colors.less

@@ -120,3 +120,6 @@
 
 @active__color: @theme__color__secondary;
 @error__color: @color-red10;
+
+@deprecated__light_color: #faecec;
+@deprecated__dark_color: #d6474a;