[file_packager] Remove unused errback fetchRemovePackage. NFC

This argument has basically used since 3839dd4.

Even when this function was first add in 74f3242 the errback
callback was only used for the IDB failures, not the fetch failures.
Fetch failure were left to propagate to the global error handlers.

The exception here was that when node support was added in #11785 it,
I believe incorrectly used errback to handle file read errors (doesn't
match the web version that does *not* handle fetch error using errback).

This is small cleanup in advance of #24893.

Author: sbc100

tools/file_packager.py

@@ -953,18 +953,12 @@ def generate_js(data_target, data_files, metadata):
     if options.support_node:
       node_support_code = '''
         if (isNode) {
-          require('fs').readFile(packageName, (err, contents) => {
-            if (err) {
-              errback(err);
-            } else {
-              callback(contents.buffer);
-            }
-          });
+          require('fs/promises').readFile(packageName).then((contents) => callback(contents.buffer));
           return;
         }'''.strip()
 
     ret += '''
-      function fetchRemotePackage(packageName, packageSize, callback, errback) {
+      function fetchRemotePackage(packageName, packageSize, callback) {
         %(node_support_code)s
         Module['dataFileDownloads'] ??= {};
         fetch(packageName)
@@ -1040,7 +1034,7 @@ def generate_js(data_target, data_files, metadata):
         function preloadFallback(error) {
           console.error(error);
           console.error('falling back to default preload behavior');
-          fetchRemotePackage(REMOTE_PACKAGE_NAME, REMOTE_PACKAGE_SIZE, processPackageData, handleError);
+          fetchRemotePackage(REMOTE_PACKAGE_NAME, REMOTE_PACKAGE_SIZE, processPackageData);
         };
 
         openDatabase()
@@ -1059,8 +1053,7 @@ def generate_js(data_target, data_files, metadata):
                         console.error(error);
                         processPackageData(packageData);
                       });
-                  }
-                , preloadFallback);
+                  });
               }
             })
           }).catch(preloadFallback);
@@ -1082,7 +1075,7 @@ def generate_js(data_target, data_files, metadata):
         } else {
           fetched = data;
         }
-      }, handleError);\n'''
+      });\n'''
 
       code += '''
       Module['preloadResults'][PACKAGE_NAME] = {fromCache: false};