docs: delete no longer needed file

These files were used by the theming of the old website, and is no
longer needed.

Reviewed-by: Eric Engestrom <eric@engestrom.ch>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4630>

docs/mesa.css

@@ -1,64 +0,0 @@
-/* Mesa CSS */
-body {
-	background-color: #ffffff;
-	font: 14px 'Lucida Grande', Geneva, Arial, Verdana, sans-serif;
-	color: black;
-}
-
-h1 {
-	font-size: 24px;
-	font-weight: bold;
-}
-
-h2 {
-	font-size: 18px;
-	font-weight: bold;
-}
-
-code {
-	font-family: monospace;
-	font-size: 10pt;
-}
-
-pre {
-	font-size: 10pt;
-	background-color: #eee;
-	margin-left: 2em;
-	padding: .5em;
-}
-
-iframe {
-	width: 19em;
-	height: 80em;
-	border: none;
-	float: left;
-}
-
-figure {
-	margin: 0.5em;
-	padding: 0.5em;
-	border: 1px solid #ccc;
-}
-
-figure pre {
-	margin: 0;
-}
-
-figure figcaption {
-	padding-top: 0.5em;
-}
-
-.content {
-	position: absolute;
-	left: 20em;
-	right: 10px;
-	overflow: hidden;
-}
-
-.header {
-	background: url('gears.png') 15px no-repeat, black url('gears.png') right no-repeat;
-	padding: 1.75rem;
-	text-align: center;
-	color: white;
-	font: x-large sans-serif;
-}