Remove notification stylesheet

These were currently undocumented in the styleguide, had hard-coded colors,
weren't being styled by the default light/dark UI themes, and were unused.

They were also causing conflicts with the notification token scope that
the Objective-C grammar uses.

static/atom.less

@@ -20,7 +20,6 @@
 @import "overlay";
 @import "lists";
 @import "popover-list";
-@import "notification";
 @import "messages";
 @import "markdown";
 @import "editor";

static/notification.less

@@ -1,56 +0,0 @@
-.notification {
-  position: absolute;
-  top: 40px;
-  left: 50%;
-  margin-left: -5%;
-  z-index: 9999;
-  border: 2px solid rgba(0, 0, 0, 0.2);
-  border-radius: 5px;
-  box-shadow:
-    inset 1px 1px 0 rgba(255, 255, 255, 0.05),
-    0 0 5px rgba(0, 0, 0, 0.5);
-  background: -webkit-linear-gradient(
-    rgba(20, 20, 20, 0.5),
-    rgba(0, 0, 0, 0.5));
-  color: #eee;
-  width: 300px;
-}
-
-.notification .content {
-  padding: 10px;
-  margin-left: 42px;
-  box-sizing: border-box;
-}
-
-.notification .content:after {
-  content: ".";
-  display: block;
-  clear: both;
-  visibility: hidden;
-}
-
-.notification .title {
-  font-size: 12px;
-  font-weight: bold;
-  margin-bottom: 3px;
-}
-
-.notification .message {
-  font-size: 12px;
-  color: #777;
-}
-
-.notification .icon {
-  display: inline-block;
-  font-family: 'Octicons Regular';
-  font-size: 32px;
-  width: 32px;
-  height: 32px;
-  margin-right: 5px;
-  -webkit-font-smoothing: antialiased;
-}
-
-/* TODO: Full Octicon Support */
-.icon-gist {
-  content: "\f20e";
-}