Fix some old references to src/worker.js. NFC

src/library_pthread.js

@@ -134,7 +134,7 @@ var LibraryPThread = {
       // pthread_join to them would block forever.
       // pthreads can still choose to set `noExitRuntime` explicitly, or
       // call emscripten_unwind_to_js_event_loop to extend their lifetime beyond
-      // their main function.  See comment in src/worker.js for more.
+      // their main function.  See comment in src/runtime_pthread.js for more.
       noExitRuntime = false;
 #endif
     },

system/lib/pthread/thread_mailbox.c

@@ -70,7 +70,7 @@ void _emscripten_thread_mailbox_init(pthread_t thread) {
   thread->waiting_async = 0;
 }
 
-// Exported for use in worker.js, but otherwise an internal function.
+// Internal function, called from runtime_pthread.js
 void _emscripten_check_mailbox() {
   // Before we attempt to execute a request from another thread make sure we
   // are in sync with all the loaded code.

tools/link.py

@@ -482,7 +482,7 @@ def setup_pthreads():
 
   default_setting('DEFAULT_PTHREAD_STACK_SIZE', settings.STACK_SIZE)
 
-  # Functions needs to be exported from the module since they are used in worker.js
+  # Functions needs by runtime_pthread.js
   settings.REQUIRED_EXPORTS += [
     '_emscripten_thread_free_data',
     '_emscripten_thread_crashed',