Remove all dropdown animations and set display: none if they're not open

app/assets/stylesheets/framework/dropdowns.scss

@@ -16,20 +16,12 @@
 
 @mixin set-visible {
   transform: translateY(0);
-  visibility: visible;
-  opacity: 1;
-  transition-duration: 100ms, 150ms, 25ms;
-  transition-delay: 35ms, 50ms, 25ms;
+  display: block;
 }
 
 @mixin set-invisible {
   transform: translateY(-10px);
-  visibility: hidden;
-  opacity: 0;
-  transition-property: opacity, transform, visibility;
-  transition-duration: 70ms, 250ms, 250ms;
-  transition-timing-function: linear, $dropdown-animation-timing;
-  transition-delay: 25ms, 50ms, 0ms;
+  display: none;
 }
 
 .open {

app/assets/stylesheets/pages/issuable.scss

@@ -499,10 +499,6 @@
 
 .with-performance-bar .right-sidebar {
   top: $header-height + $performance-bar-height;
-
-  .issuable-sidebar {
-    height: calc(100% - #{$header-height} - #{$performance-bar-height});
-  }
 }
 
 .sidebar-move-issue-confirmation-button {