DevTools: fix style nits in auto-attach tests

This is a follow-up fix to address comments from https://crrev.com/c/2042302

Bug: 1051687
Change-Id: Id6bc1ed057b85d8ed66b42378825a47ce7775170
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2071360Reviewed-by: Peter Marshall <petermarshall@chromium.org>
Commit-Queue: Yury Semikhatsky <yurys@chromium.org>
Cr-Commit-Position: refs/heads/master@{#748838}

third_party/blink/web_tests/http/tests/inspector-protocol/target/target-setAutoAttach-about-blank.js

 (async function(testRunner) {
-  var {page, session, dp} = await testRunner.startBlank(
+  await testRunner.startBlank(
       `Tests that browser.Target.setAutoAttach() attaches to new about:blank page.`);
 
   const target = testRunner.browserP().Target;

third_party/blink/web_tests/http/tests/inspector-protocol/target/target-setAutoAttach-flatten-only-expected.txt

 Tests that browser.Target.setAutoAttach() supports only flatten protocol.
-Tried to auto-attach with not fatten protocol{
+Tried to auto-attach with not flatten protocol{
     error : {
         code : -32602
         message : Only flatten protocol is supported with browser level auto-attach

third_party/blink/web_tests/http/tests/inspector-protocol/target/target-setAutoAttach-flatten-only.js

 (async function(testRunner) {
-  var {page, session, dp} = await testRunner.startBlank(
+  await testRunner.startBlank(
       `Tests that browser.Target.setAutoAttach() supports only flatten protocol.`);
 
   const target = testRunner.browserP().Target;
   const response = await target.setAutoAttach(
       {autoAttach: true, waitForDebuggerOnStart: true, flatten: false});
-  testRunner.log(response, 'Tried to auto-attach with not fatten protocol');
+  testRunner.log(response, 'Tried to auto-attach with not flatten protocol');
 
   testRunner.completeTest();
 })

third_party/blink/web_tests/http/tests/inspector-protocol/target/target-setAutoAttach-new-page.js

 (async function(testRunner) {
-  var {page, session, dp} = await testRunner.startBlank(
+  await testRunner.startBlank(
       `Tests that browser.Target.setAutoAttach() attaches to new page targets.`);
 
   const target = testRunner.browserP().Target;

third_party/blink/web_tests/http/tests/inspector-protocol/target/target-setAutoAttach-windowOpen.js

 (async function(testRunner) {
-  var {page, session, dp} = await testRunner.startBlank(
+  const {page, session, dp} = await testRunner.startBlank(
       `Tests that browser.Target.setAutoAttach() attaches to window.open targets.`);
 
   const target = testRunner.browserP().Target;