Loki: do not special-case __name__ label (#47251)

* loki: do not mutate the caller's data

* Update public/app/plugins/datasource/loki/result_transformer.ts

better comment

Co-authored-by: Ivana Huckova <30407135+ivanahuckova@users.noreply.github.com>

* Update public/app/plugins/datasource/loki/result_transformer.ts

no need to handle __name__

Co-authored-by: Ivana Huckova <30407135+ivanahuckova@users.noreply.github.com>

* simplify code

Co-authored-by: Ivana Huckova <30407135+ivanahuckova@users.noreply.github.com>

public/app/plugins/datasource/loki/result_transformer.ts

@@ -290,12 +290,10 @@ export function createMetricLabel(labelData: { [key: string]: string }, options?
 }
 
 function getOriginalMetricName(labelData: { [key: string]: string }) {
-  const metricName = labelData.__name__ || '';
-  delete labelData.__name__;
   const labelPart = Object.entries(labelData)
     .map((label) => `${label[0]}="${label[1]}"`)
     .join(',');
-  return `${metricName}{${labelPart}}`;
+  return `{${labelPart}}`;
 }
 
 export function decamelize(s: string): string {