remove unused code

style/components/collapse.less

@@ -10,10 +10,10 @@
 .@{collapse-prefix-cls} {
   background-color: #f4f4f4;
   border-radius: 3px;
-  border: 1px solid #d9d9d9;
+  border: 1px solid @border-color-base;
 
   & > &-item {
-    border-top: 1px solid #d9d9d9;
+    border-top: 1px solid @border-color-base;
     &:first-child {
       border-top: 0;
     }
@@ -65,11 +65,6 @@
     }
   }
 
-  &-collapsing {
-    transition-duration: .24s;
-    transition-timing-function: @ease-out-circ;
-  }
-
   &-item:last-child {
     > .@{collapse-prefix-cls}-content {
       border-radius: 0 0 3px 3px;