style: decentralized less var (#8369)

* style: decentralized less var

* chore: remove emtpy var file

src/progress/index.less

@@ -1,4 +1,4 @@
-@import '../style/var.less';
+@import './var.less';
 
 .van-progress {
   position: relative;

src/progress/var.less

@@ -0,0 +1,10 @@
+@import '../style/var.less';
+
+@progress-height: 4px;
+@progress-color: @blue;
+@progress-background-color: @gray-3;
+@progress-pivot-padding: 0 5px;
+@progress-pivot-text-color: @white;
+@progress-pivot-font-size: @font-size-xs;
+@progress-pivot-line-height: 1.6;
+@progress-pivot-background-color: @blue;