Stop creating sinon sandbox early

sinon might not be loaded at this point, which can cause tests to fail.

We could create the sandbox in one of the hooks instead, but let's
remove the sandbox completely to stay consistent with our other tests.

tests/test.webutil.js

@@ -180,16 +180,15 @@ describe('WebUtil', function () {
                 window.chrome = chrome;
             });
 
-            const csSandbox = sinon.createSandbox();
-
             beforeEach(function () {
                 settings = {};
-                csSandbox.spy(window.chrome.storage.sync, 'set');
-                csSandbox.spy(window.chrome.storage.sync, 'remove');
+                sinon.spy(window.chrome.storage.sync, 'set');
+                sinon.spy(window.chrome.storage.sync, 'remove');
                 return WebUtil.initSettings();
             });
             afterEach(function () {
-                csSandbox.restore();
+                window.chrome.storage.sync.set.restore();
+                window.chrome.storage.sync.remove.restore();
             });
 
             describe('writeSetting', function () {