remove restriction on running parallel decodeSingle

- surprisingly, this seems to work

src/quagga.js

@@ -7,7 +7,6 @@ import ImageDebug from './common/image_debug';
 import ResultCollector from './analytics/result_collector';
 import Config from './config/config';
 import { merge } from 'lodash';
-import * as QWorkers from './quagga/qworker.ts';
 
 import Quagga from './quagga/quagga';
 
@@ -66,21 +65,6 @@ export default {
     canvas: _context.canvasContainer,
     decodeSingle: function (config, resultCallback) {
         const quaggaInstance = new Quagga();
-        if (this.inDecodeSingle) {
-            // force multiple calls to decodeSingle to run in serial, because presently
-            // simultaneous running breaks things.
-            if (resultCallback) {
-                setTimeout(() => this.decodeSingle(config, resultCallback), 300);
-            } else {
-                return new Promise((resolve) => {
-                    setTimeout(() => this.decodeSingle(config, (res) => {
-                        resolve(res);
-                    }, 300));
-                });
-            }
-            return null;
-        }
-        // this.inDecodeSingle = true;
         config = merge({
             inputStream: {
                 type: 'ImageStream',
@@ -108,7 +92,6 @@ export default {
             try {
                 this.init(config, () => {
                     Events.once('processed', (result) => {
-                        this.inDecodeSingle = false;
                         quaggaInstance.stop();
                         if (resultCallback) {
                             resultCallback.call(null, result);
@@ -118,7 +101,6 @@ export default {
                     quaggaInstance.start();
                 }, null, quaggaInstance);
             } catch (err) {
-                this.inDecodeSingle = false;
                 reject(err);
             }
         });