fix(aio): tidy up layout of api filter page

* Remove the "info-banner" styling from the filters.
* Fix alignment of the search box on a narrow screen (closes #17395)
* Remove unnecessary whitespace before section headers

aio/src/app/embedded/api/api-list.component.html

@@ -1,4 +1,4 @@
-<div class="l-flex-wrap info-banner api-filter">
+<div class="l-flex-wrap api-filter">
 
   <aio-select (change)="setType($event.option)"
               [options]="types"