Revert "Rename FileReader.readAsText second parameter from 'label' to 'encoding' (#25797)"

This reverts commit eaf4f92.

Author: chozzz

lib/lib.dom.d.ts

@@ -5033,7 +5033,7 @@ interface FileReader extends EventTarget {
     readAsArrayBuffer(blob: Blob): void;
     readAsBinaryString(blob: Blob): void;
     readAsDataURL(blob: Blob): void;
-    readAsText(blob: Blob, encoding?: string): void;
+    readAsText(blob: Blob, label?: string): void;
     readonly DONE: number;
     readonly EMPTY: number;
     readonly LOADING: number;

lib/lib.webworker.d.ts

@@ -1217,7 +1217,7 @@ interface FileReader extends EventTarget {
     readAsArrayBuffer(blob: Blob): void;
     readAsBinaryString(blob: Blob): void;
     readAsDataURL(blob: Blob): void;
-    readAsText(blob: Blob, encoding?: string): void;
+    readAsText(blob: Blob, label?: string): void;
     readonly DONE: number;
     readonly EMPTY: number;
     readonly LOADING: number;