Revert "[iOS] Reenable testXClientData"

This reverts commit faad9f7d.

Reason for revert: Test is constantly failing on iPad device.
https://crbug.com/1059256

Original change's description:
> [iOS] Reenable testXClientData
> 
> This CL re-enable testXClientData as it was probably failing because of
> a DCHECK in WebController, that should have been fixed in
> crrev.com/c/1992063.
> 
> Fixed: 1036225
> Change-Id: Id9a85c0f35310e79adcf030d222cce2e9e36274b
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1993813
> Commit-Queue: Gauthier Ambard <gambard@chromium.org>
> Reviewed-by: Stepan Khapugin <stkhapugin@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#731180}

TBR=stkhapugin@chromium.org,gambard@chromium.org

# Not skipping CQ checks because original CL landed > 1 day ago.

Change-Id: I46f969294cb515e38df34df3f6ed66e4fc9ec558
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2091711Reviewed-by: Sergio Collazos <sczs@chromium.org>
Commit-Queue: Sergio Collazos <sczs@chromium.org>
Cr-Commit-Position: refs/heads/master@{#747810}

ios/chrome/browser/ui/omnibox/omnibox_egtest.mm

@@ -150,7 +150,8 @@ id<GREYMatcher> SearchCopiedTextButton() {
 
 // Tests that the XClientData header is sent when navigating to
 // https://google.com through the omnibox.
-- (void)testXClientData {
+// TODO(crbug.com/1036225): Test very flaky on all config.
+- (void)DISABLED_testXClientData {
   // Rewrite the google URL to localhost URL.
   [OmniboxAppInterface rewriteGoogleURLToLocalhost];