message: Remove redundant extra chevrons from ContextualMenu
  This removes a seemingly redundant layer of extra chevrons from
  `ContextualMenu`. Since both chevrons are the same color, there should be no
  visual change.
diff: /*
  Copyright 2015, 2016 OpenMarket Ltd
  +Copyright 2019 The Matrix.org Foundation C.I.C.
  Licensed under the Apache License, Version 2.0 (the "License");
  you may not use this file except in compliance with the License.
  @@ -58,18 +59,6 @@ limitations under the License.
  border-bottom: 8px solid transparent;
  }
  -.mx_ContextualMenu_chevron_right::after {
  - content: '';
  - width: 0;
  - height: 0;
  - border-top: 7px solid transparent;
  - border-left: 7px solid $menu-bg-color;
  - border-bottom: 7px solid transparent;
  - position: absolute;
  - top: -7px;
  - right: 1px;
  -}
  -
  .mx_ContextualMenu_left {
  left: 0;
  }
  @@ -89,18 +78,6 @@ limitations under the License.
  border-bottom: 8px solid transparent;
  }
  -.mx_ContextualMenu_chevron_left::after {
  - content: '';
  - width: 0;
  - height: 0;
  - border-top: 7px solid transparent;
  - border-right: 7px solid $menu-bg-color;
  - border-bottom: 7px solid transparent;
  - position: absolute;
  - top: -7px;
  - left: 1px;
  -}
  -
  .mx_ContextualMenu_top {
  top: 0;
  }
  @@ -120,18 +97,6 @@ limitations under the License.
  border-right: 8px solid transparent;
  }
  -.mx_ContextualMenu_chevron_top::after {
  - content: '';
  - width: 0;
  - height: 0;
  - border-left: 7px solid transparent;
  - border-bottom: 7px solid $menu-bg-color;
  - border-right: 7px solid transparent;
  - position: absolute;
  - left: -7px;
  - top: 1px;
  -}
  -
  .mx_ContextualMenu_bottom {
  bottom: 0;
  }
  @@ -151,18 +116,6 @@ limitations under the License.
  border-right: 8px solid transparent;
  }
  -.mx_ContextualMenu_chevron_bottom::after {
  - content: '';
  - width: 0;
  - height: 0;
  - border-left: 7px solid transparent;
  - border-top: 7px solid $menu-bg-color;
  - border-right: 7px solid transparent;
  - position: absolute;
  - left: -7px;
  - bottom: 1px;
  -}
  -
  .mx_ContextualMenu_spinner {
  display: block;
  margin: 0 auto;
  