Revert "fix: prevent side-effect from .stack-for in media-object"

This reverts commit 606f164.

> Prevent a parent component with `.stack-for-*` to have side effects on `.media-object-section`.
Actually, no others component uses `.stack-for-*`.

Also, this would prevent to create a custom component from `@media media-object-section`.

scss/components/_media-object.scss

@@ -38,12 +38,6 @@ $mediaobject-image-width-stacked: 100% !default;
       }
     }
   }
-
-  &.stack-for-#{$-zf-zero-breakpoint} .media-object-section {
-    @include breakpoint($-zf-zero-breakpoint only) {
-      @include media-object-stack;
-    }
-  }
 }
 
 /// Adds styles for sections within a media object.
@@ -69,6 +63,12 @@ $mediaobject-image-width-stacked: 100% !default;
     margin-bottom: 0;
   }
 
+  .stack-for-#{$-zf-zero-breakpoint} & {
+    @include breakpoint($-zf-zero-breakpoint only) {
+      @include media-object-stack;
+    }
+  }
+
   @if $global-flexbox {
     &.main-section {
       flex: 1 1 0px; // sass-lint:disable-line zero-unit