Theme: update icon (#15257)

packages/theme-chalk/src/icon.scss

@@ -557,10 +557,6 @@
   content: "\e72b";
 }
 
-.el-icon-open-mail:before {
-  content: "\e72c";
-}
-
 .el-icon-chat-line-square:before {
   content: "\e72d";
 }
@@ -1181,10 +1177,6 @@
   content: "\e7c7";
 }
 
-.el-icon-platform-baidu:before {
-  content: "\e7c8";
-}
-
 .el-icon-delete-solid:before {
   content: "\e7c9";
 }