removed max-height transition until it can be done without bad effects on long forms

wagtail/wagtailadmin/static/wagtailadmin/scss/components/forms.scss

@@ -304,9 +304,7 @@ input[type=submit], input[type=reset], input[type=button], button{
 }
 
 .multiple{
-    @include transition(max-height 10s ease);
     padding:0;
-    max-height:10000px;
     max-width:1024px - 50px;
     overflow:hidden;
 

wagtail/wagtailadmin/static/wagtailadmin/scss/layouts/page-editor.scss

@@ -269,7 +269,6 @@
 
         .multiple{
             padding:0;
-            max-height:0px;
         }
     }