Revert "[ MimeHandlerView ] Fix an error in test"

This reverts commit 0634e8dd.

Reason for revert: MimeHandlerViewCrossProcessTest.NavigationRaceFromCrossProcessRenderer is failing on Mac bots
crbug.com/927564

Original change's description:
> [ MimeHandlerView ] Fix an error in test
> 
> The |query_index| was not defined and the test was not actually
> navigating the test page to the desired URL.
> 
> TBR=wjmaclean@chromium.org
> 
> Bug: 659750
> Change-Id: I8f9658ac80adaa20f3cdceb0c19f799b59f96987
> Reviewed-on: https://chromium-review.googlesource.com/c/1448776
> Reviewed-by: Ehsan Karamad <ekaramad@chromium.org>
> Commit-Queue: Ehsan Karamad <ekaramad@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#628125}

TBR=ekaramad@chromium.org,wjmaclean@chromium.org

Change-Id: Iae21364b81a5a031c96ba6342b5ffa9186e21076
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 659750
Reviewed-on: https://chromium-review.googlesource.com/c/1448087Reviewed-by: Keishi Hattori <keishi@chromium.org>
Commit-Queue: Keishi Hattori <keishi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#628227}

chrome/test/data/extensions/api_test/mime_handler_view/test_page.html

@@ -7,7 +7,6 @@
     const token = "?next=";
     if (!query.startsWith(token))
       return false;
-    let query_index = query.indexOf(token);
     window.location.href = query.substr(query_index + token.length);
     return true;
   }