Revert "Disabling PasswordsSettingsTestCase/testEditUsernameFails for device iOS"

This reverts commit 8bbcdd00.

Reason for revert: Causes compilation failure on iOS
https://ci.chromium.org/p/chromium/builders/ci/ios-device/170093?

Original change's description:
> Disabling PasswordsSettingsTestCase/testEditUsernameFails for device iOS
>
> The test fails iPad 6th on iOS 12.4.
>
> Bug: 1140400
> Change-Id: Ic4016aee1ad1444af112a4c1ceb34e7829533758
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2485934
> Commit-Queue: Jérôme Lebel <jlebel@chromium.org>
> Auto-Submit: Jérôme Lebel <jlebel@chromium.org>
> Reviewed-by: Viktor Semeniuk <vsemeniuk@google.com>
> Cr-Commit-Position: refs/heads/master@{#818868}

TBR=jlebel@chromium.org,vsemeniuk@google.com

Change-Id: Ie20ef9089f8da8ba7345ccc99391ea22233d0b5f
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 1140400
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2485938Reviewed-by: Andy Paicu <andypaicu@chromium.org>
Commit-Queue: Andy Paicu <andypaicu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#818870}

ios/chrome/browser/ui/settings/password/passwords_settings_egtest.mm

@@ -1484,13 +1484,7 @@ void CopyPasswordDetailWithID(int detail_id) {
 
 // Checks that attempts to edit a username to a value which is already used for
 // the same domain fails.
-// TODO(crbug.com/1140400): Fails on device for iPad 6th iOS 12.4.
-#if TARGET_IPHONE_SIMULATOR
-#define MAYBE_testEditUsernameFails testEditUsernameFails
-#else
-#define MAYBE_testEditUsernameFails DISABLED_testEditUsernameFails
-#endif
-- (void)MAYBE_testEditUsernameFails {
+- (void)testEditUsernameFails {
   GREYAssert(
       [PasswordSettingsAppInterface saveExamplePassword:@"concrete password"
                                                userName:@"concrete username1"