fix: Button.Group size style issue (#21307)

* remove useless fixing line-height

* update snapshot

components/button/__tests__/__snapshots__/demo.test.js.snap

@@ -509,6 +509,77 @@ exports[`renders ./components/button/demo/icon.md correctly 1`] = `
 </div>
 `;
 
+exports[`renders ./components/button/demo/legacy-group.md correctly 1`] = `
+<div>
+  <div>
+    <div
+      class="ant-btn-group ant-btn-group-sm"
+    >
+      <button
+        class="ant-btn ant-btn-primary"
+        type="button"
+      >
+        <span>
+          Button 1
+        </span>
+      </button>
+      <button
+        class="ant-btn ant-btn-primary"
+        type="button"
+      >
+        <span>
+          Button 2
+        </span>
+      </button>
+    </div>
+  </div>
+  <div>
+    <div
+      class="ant-btn-group"
+    >
+      <button
+        class="ant-btn ant-btn-primary"
+        type="button"
+      >
+        <span>
+          Button 1
+        </span>
+      </button>
+      <button
+        class="ant-btn ant-btn-primary"
+        type="button"
+      >
+        <span>
+          Button 2
+        </span>
+      </button>
+    </div>
+  </div>
+  <div>
+    <div
+      class="ant-btn-group ant-btn-group-lg"
+    >
+      <button
+        class="ant-btn ant-btn-primary"
+        type="button"
+      >
+        <span>
+          Button 1
+        </span>
+      </button>
+      <button
+        class="ant-btn ant-btn-primary"
+        type="button"
+      >
+        <span>
+          Button 2
+        </span>
+      </button>
+    </div>
+  </div>
+</div>
+`;
+
 exports[`renders ./components/button/demo/loading.md correctly 1`] = `
 <div>
   <button

components/button/demo/legacy-group.md

@@ -0,0 +1,39 @@
+---
+order: 99
+title:
+  zh-CN: 废弃的 Block 组
+  en-US: Deprecated Button Group
+debug: true
+---
+
+## zh-CN
+
+Debug usage
+
+## en-US
+
+Debug usage
+
+```jsx
+import { Button } from 'antd';
+
+function getGroup(props) {
+  return (
+    <div>
+      <Button.Group {...props}>
+        <Button type="primary">Button 1</Button>
+        <Button type="primary">Button 2</Button>
+      </Button.Group>
+    </div>
+  );
+}
+
+ReactDOM.render(
+  <div>
+    {getGroup({ size: 'small' })}
+    {getGroup()}
+    {getGroup({ size: 'large' })}
+  </div>,
+  mountNode,
+);
+```

components/button/style/mixin.less

@@ -185,7 +185,6 @@
   &-lg > .@{btnClassName},
   &-lg > span > .@{btnClassName} {
     .button-size(@btn-height-lg; @btn-padding-horizontal-lg; @btn-font-size-lg; 0);
-    line-height: @btn-height-lg - 2px;
   }
   &-lg > .@{btnClassName}.@{btnClassName}-icon-only {
     .square(@btn-height-lg);
@@ -195,7 +194,6 @@
   &-sm > .@{btnClassName},
   &-sm > span > .@{btnClassName} {
     .button-size(@btn-height-sm; @btn-padding-horizontal-sm; @font-size-base; 0);
-    line-height: @btn-height-sm - 2px;
     > .@{iconfont-css-prefix} {
       font-size: @font-size-base;
     }