Remove mention of popovers auto placement + add note to migration docs

docs/components/popovers.md

@@ -218,7 +218,7 @@ Options can be passed via data attributes or JavaScript. For data attributes, ap
         <td>string | function</td>
         <td>'right'</td>
         <td>
-          <p>How to position the popover - top | bottom | left | right | auto.<br>When "auto" is specified, it will dynamically reorient the popover. For example, if placement is "auto left", the popover will display to the left when possible, otherwise it will display right.</p>
+          <p>How to position the popover - top | bottom | left | right.</p>
           <p>When a function is used to determine the placement, it is called with the popover DOM node as its first argument and the triggering element DOM node as its second. The <code>this</code> context is set to the popover instance.</p>
         </td>
       </tr>

docs/migration.md

@@ -181,6 +181,10 @@ Dropped entirely for the new card component.
 
 - Removed support for `auto` placement options.
 
+### Popovers
+
+- Removed support for `auto` placement options.
+
 ### Carousel
 
 - Overhauled the entire component to simplify design and styling. We have fewer styles for you to override, new indicators, and new icons.