Remove unused prop in `ElOption`. (#2730)

* Fix lint error.

* Remove unused prop.

packages/loading/src/loading.vue

@@ -31,4 +31,4 @@
       }
     }
   };
-</script>
+</script>

packages/select/src/option.vue

@@ -30,10 +30,6 @@
         required: true
       },
       label: [String, Number],
-      selected: {
-        type: Boolean,
-        default: false
-      },
       created: Boolean,
       disabled: {
         type: Boolean,

packages/tabs/src/tab-bar.vue

@@ -39,4 +39,4 @@
       }
     }
   };
-</script>
+</script>