Removed unused code from datasource.js

public/app/plugins/datasource/opentsdb/datasource.js

@@ -14,10 +14,6 @@ function (angular, _, dateMath) {
     this.name = instanceSettings.name;
     this.withCredentials = instanceSettings.withCredentials;
     this.basicAuth = instanceSettings.basicAuth;
-    this.tsdbVersions = [
-      {name: '<=2.1', value: 1},
-      {name: '>=2.2', value: 2},
-    ];
     this.tsdbVersion = instanceSettings.jsonData.tsdbVersion;
     this.supportMetrics = true;
     this.tagKeys = {};