Remove the makeReasonSerializable helper function, and use wrapReason instead, in src/shared/message_handler.js

Since `wrapReason` and `makeReasonSerializable` are essentially functionally equivalent it doesn't seem necessary to keep both of them around, especially when `makeReasonSerializable` only has a *single* call-site.

src/shared/message_handler.js

@@ -48,22 +48,13 @@ function wrapReason(reason) {
       return new MissingPDFException(reason.message);
     case 'UnexpectedResponseException':
       return new UnexpectedResponseException(reason.message, reason.status);
-    default:
+    case 'UnknownErrorException':
       return new UnknownErrorException(reason.message, reason.details);
+    default:
+      return new UnknownErrorException(reason.message, reason.toString());
   }
 }
 
-function makeReasonSerializable(reason) {
-  if (!(reason instanceof Error) ||
-      reason instanceof AbortException ||
-      reason instanceof MissingPDFException ||
-      reason instanceof UnexpectedResponseException ||
-      reason instanceof UnknownErrorException) {
-    return reason;
-  }
-  return new UnknownErrorException(reason.message, reason.toString());
-}
-
 function resolveOrReject(capability, data) {
   if (data.success) {
     capability.resolve();
@@ -125,7 +116,7 @@ function MessageHandler(sourceName, targetName, comObj) {
             targetName,
             isReply: true,
             callbackId: data.callbackId,
-            error: makeReasonSerializable(reason),
+            error: wrapReason(reason),
           });
         });
       } else if (data.streamId) {