Revert "[iOS] Fix broken tests due to missing completion in fake ViewController."

This reverts commit cf4e7dcb.

Reason for revert: AddAccountSigninManagerTests are failing again

Original change's description:
> [iOS] Fix broken tests due to missing completion in fake ViewController.
> 
> AddAccountSigninManagerTests were failing due to a missing run
> completion. Remove intermediary method that causes this failure.
> 
> Bug: 1078815
> Change-Id: I1766e593927cd40be318cf66bb67d11f5ed47006
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2264057
> Commit-Queue: Jérôme Lebel <jlebel@chromium.org>
> Reviewed-by: Jérôme Lebel <jlebel@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#782928}

TBR=jlebel@chromium.org,fernandex@chromium.org

Change-Id: I13a4ea3529c35567c607eeb77ce9e9c690ac8cbe
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 1078815
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2269879
Commit-Queue: Lindsay Pasricha <lindsayw@chromium.org>
Reviewed-by: Eugene But <eugenebut@chromium.org>
Cr-Commit-Position: refs/heads/master@{#783006}

ios/chrome/browser/ui/authentication/signin/signin_coordinator_egtest.mm

@@ -496,7 +496,8 @@ void ChooseImportOrKeepDataSepareteDialog(id<GREYMatcher> choiceButtonMatcher) {
   [SigninEarlGreyUtils
       waitForMatcher:grey_accessibilityID(kFakeAddAccountViewIdentifier)];
   // Close the SSO view controller.
-  id<GREYMatcher> matcher = grey_allOf(ButtonWithAccessibilityLabel(@"Cancel"),
+  id<GREYMatcher> matcher =
+      grey_allOf(chrome_test_util::ButtonWithAccessibilityLabel(@"Cancel"),
                  grey_sufficientlyVisible(), nil);
   [[EarlGrey selectElementWithMatcher:matcher] performAction:grey_tap()];
   // Make sure the SSO view controller is fully removed before ending the test.
@@ -514,14 +515,11 @@ void ChooseImportOrKeepDataSepareteDialog(id<GREYMatcher> choiceButtonMatcher) {
   [SigninEarlGreyUI tapAddAccountButton];
 
   [self assertFakeSSOScreenIsVisible];
-
   // Close sign-in screen and Settings.
   [[EarlGrey selectElementWithMatcher:
                  ButtonWithAccessibilityLabelId(
                      IDS_IOS_ACCOUNT_CONSISTENCY_SETUP_SKIP_BUTTON)]
       performAction:grey_tap()];
-  [[EarlGrey selectElementWithMatcher:SettingsDoneButton()]
-      performAction:grey_tap()];
   [[GREYUIThreadExecutor sharedInstance] drainUntilIdle];
 }
 

ios/public/provider/chrome/browser/signin/fake_chrome_identity_interaction_manager.mm

@@ -146,7 +146,7 @@
     [self runCompletionCallbackWithError:error];
     return;
   }
-  [_viewController
+  [self.delegate interactionManager:self
       dismissViewControllerAnimated:animated
                          completion:^{
                            [self runCompletionCallbackWithError:error];