Remove the warning about the grid rename

It's been long enough and we no longer provide the shim.

Author: aaronshekey

docs/product/base/grid.html

@@ -5,11 +5,6 @@
 ---
 <section class="stacks-section">
     {% header "h2", "Overview" %}
-    {% tip, "warning", "mb24" %}
-        <p>Looking for our old flex grid? <a href="{{ "/product/base/flex" | url }}">Flex layouts</a> have been moved and renamed now that CSS grid is here. Our <code class="stacks-code">.grid</code>, and <code class="stacks-code">.grid--cell</code> classes have been removed in favor of <code class="stacks-code">.d-flex</code> and <code class="stacks-code">.flex--item</code>.</p>
-        <p class="mb0">If you need to continue using the old <code class="stacks-code">.grid</code>, and <code class="stacks-code">.grid--cell</code> classes, Stacks provides a <a href="https://unpkg.com/@stackoverflow/stacks/dist/css/stacks-flexgrid-shim.min.css">shim</a> for backwards compatability.</p>
-    {% endtip %}
-
     <p class="stacks-copy">CSS Grids are the most powerful layout system available in CSS. It has two dimensions, meaning it can handle both columns and rows simultaneously, unlike <a href="{{ "/product/base/flex" | url }}">flex layouts</a> which can only do one at a time. Applying <code class="stacks-code">.d-grid</code> to a container will lay out its children according to the CSS Grid layout spec. Adding atomic modifying classes will change the layout’s behavior. Applying classes to an individual <code class="stacks-code">.grid--item</code> will change that cell’s behavior.</p>
 
     {% header "h3", "Examples" %}