back out previous bodges to flexbox to make geminiscrollbar work in FF

src/skins/vector/css/organisms/RoomView.css

@@ -105,16 +105,14 @@ limitations under the License.
     -webkit-flex: 1 1 0;
     flex: 1 1 0;
 
-    /* specify width and margin in here rather than the wrapper otherwise gemini-scrollbars gets confused */
-    min-width: 0px;
-    max-width: 960px;
     width: 100%;
-    margin: auto;
 
     overflow-y: auto;
 }
 
 .mx_RoomView_messageListWrapper {
+    max-width: 960px;
+    margin: auto;
 }
 
 .mx_RoomView_MessageList {

src/skins/vector/css/pages/MatrixChat.css

@@ -71,22 +71,13 @@ limitations under the License.
 
     background-color: #eaf5f0;
 
-/*
-    We can't use flex here as gemini-scrollbars chokes on the width calculation (on FF 42 and Chrome 48)
-    and you end up with double-scrollbars and an ever-increasing width.
-
     -webkit-flex: 0 0 210px;
     flex: 0 0 210px;
-*/
-    width: 210px;
 }
 
 .mx_MatrixChat .mx_LeftPanel.collapsed {
-/*
     -webkit-flex: 0 0 60px;
     flex: 0 0 60px;
-*/
-    width: 60px;
 }
 
 .mx_MatrixChat .mx_MatrixChat_middlePanel {
@@ -126,18 +117,11 @@ limitations under the License.
     -webkit-order: 3;
     order: 3;
 
-/*  Similarly, specify width explicitly otherwise gemini-scrollbars gets confused
-
     -webkit-flex: 0 0 235px;
     flex: 0 0 235px;
-*/
-    width: 235px;
 }
 
 .mx_MatrixChat .mx_RightPanel.collapsed {
-/*    
     -webkit-flex: 0 0 72px;
     flex: 0 0 72px;
-*/
-    width: 72px;
 }