nasmdoc.css: simplify some media queries

Some media queries were needlessly complicated and misinterpreted by
some browsers.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>

doc/nasmdoc.css

diff --git a/doc/nasmdoc.css b/doc/nasmdoc.css
index 49dc3a4..cc0b671 100644
--- a/doc/nasmdoc.css
+++ b/doc/nasmdoc.css
@@ -68,17 +68,16 @@
     vertical-align: top;
     flex: 1 1 0;
 }
-@media not screen {
-    ul.navbar {
-	display: none;
-    }
+/* This is overridden for @media screen */
+ul.navbar {
+    display: none;
 }
 @media print {
     a {
 	color: inherit;
     }
 }
-@media only screen {
+@media screen {
     div.contents {
 	-webkit-column-gap: 4em;
 	-webkit-column-rule: 1px dotted black;