Remove the extraneous notebook container widget

src/default-theme/notebook.less

@@ -4,6 +4,9 @@
 | Distributed under the terms of the Modified BSD License.
 |----------------------------------------------------------------------------*/
 .jp-Notebook {
+  padding-left: 4px;
+  padding-right: 4px;
+  padding-bottom: 20px;
   margin-top: 20px;
   min-width: 50px;
   min-height: 50px;
@@ -17,15 +20,6 @@
 }
 
 
-.jp-Notebook-container {
-  display: flex;
-  flex-direction: column;
-  padding-left: 10px;
-  padding-right: 10px;
-  padding-bottom: 20px;
-}
-
-
 .jp-InputArea-prompt {
   flex-basis: 90px;
   color: #303F9F;

src/notebook/base.less

@@ -16,11 +16,6 @@
 }
 
 
-.jp-Notebook-container {
-  flex: 1 1 auto;
-}
-
-
 .jp-InputArea {
   display: flex;
   flex-direction: row;

src/notebook/notebook/panel.ts

@@ -22,7 +22,7 @@ import {
 } from 'phosphor/lib/core/token';
 
 import {
-  Panel, PanelLayout
+  PanelLayout
 } from 'phosphor/lib/ui/panel';
 
 import {