Stop registering an onProgress callback on the PDFWorkerStreamRangeReader-instance, in the ChunkedStreamManager class

Given that nothing in the `PDFWorkerStreamRangeReader` class attempts to invoke the `onProgress` callback, this is effectively dead code now.
Looking briefly at the history of this code it's not clear, at least to me, when this became unused however it's probably close to a decade ago.

Finally, note also how progress is already being reported through the `ChunkedStreamManager.prototype.onReceiveData` method.

Author: Snuffleupagus

src/core/chunked_stream.js

@@ -283,7 +283,6 @@ class ChunkedStreamManager {
 
   sendRequest(begin, end) {
     const rangeReader = this.pdfNetworkStream.getRangeReader(begin, end);
-    rangeReader.onProgress = this.onProgress.bind(this);
 
     let chunks = [];
     return new Promise((resolve, reject) => {
@@ -441,13 +440,6 @@ class ChunkedStreamManager {
     return groupedChunks;
   }
 
-  onProgress(args) {
-    this.msgHandler.send("DocProgress", {
-      loaded: this.stream.numChunksLoaded * this.chunkSize + args.loaded,
-      total: this.length,
-    });
-  }
-
   onReceiveData(args) {
     const { chunkSize, length, stream } = this;