Cleanup test_modularize_init_error. NFC (#23105)

- Use browser_reporting.js directly.
- Delete redundant unhandledrejection handler. browser_reporting handles
this already.

test/test_browser.py

@@ -3342,9 +3342,10 @@ def test_modularize(self, opts):
       self.run_browser('a.html', '/report_result?0')
 
   def test_modularize_network_error(self):
-    browser_reporting_js_path = test_file('browser_reporting.js')
-    self.compile_btest('browser_test_hello_world.c', ['-sMODULARIZE', '-sEXPORT_NAME="createModule"', '--extern-pre-js', browser_reporting_js_path], reporting=Reporting.NONE)
+    self.compile_btest('browser_test_hello_world.c', ['-sMODULARIZE', '-sEXPORT_NAME=createModule'], reporting=Reporting.NONE)
+    shutil.copy(test_file('browser_reporting.js'), '.')
     create_file('a.html', '''
+      <script src="browser_reporting.js"></script>
       <script src="a.out.js"></script>
       <script>
         createModule()
@@ -3361,16 +3362,12 @@ def test_modularize_network_error(self):
     self.run_browser('a.html', '/report_result?Aborted(both async and sync fetching of the wasm failed)')
 
   def test_modularize_init_error(self):
-    browser_reporting_js_path = test_file('browser_reporting.js')
-    self.compile_btest('browser/test_modularize_init_error.cpp', ['-sMODULARIZE', '-sEXPORT_NAME="createModule"', '--extern-pre-js', browser_reporting_js_path], reporting=Reporting.NONE)
+    self.compile_btest('browser/test_modularize_init_error.cpp', ['-sMODULARIZE', '-sEXPORT_NAME=createModule'], reporting=Reporting.NONE)
+    shutil.copy(test_file('browser_reporting.js'), '.')
     create_file('a.html', '''
+      <script src="browser_reporting.js"></script>
       <script src="a.out.js"></script>
       <script>
-        if (typeof window === 'object') {
-          window.addEventListener('unhandledrejection', function(event) {
-            reportResultToServer("Unhandled promise rejection: " + event.reason.message);
-          });
-        }
         createModule()
           .then(() => {
             reportResultToServer("Module creation succeeded when it should have failed");