delete the .page-header and its docs

docs/components/page-header.md

----
-layout: page
-title: Page header
----
-
-A simple shell for an `h1` to appropriately space out and segment sections of content on a page. It can utilize the `h1`'s default `small` element, as well as most other components (with additional styles).
-
-## Example
-
-{% example html %}
-<div class="page-header">
-  <h1>Example page header <small>Subtext for header</small></h1>
-</div>
-{% endexample %}

scss/_type.scss

@@ -91,16 +91,6 @@ mark,
 }
 
 
-// Page header
-// -------------------------
-
-// .page-header {
-//   padding-bottom: (($line-height-computed / 2) - 1);
-//   margin: ($line-height-computed * 2) 0 @line-height-computed;
-//   border-bottom: 1px solid @page-header-border-color;
-// }
-
-
 // Lists
 // -------------------------