Remove the assertion check for closing the regular Tab.

The code which should close the regular tab was behind an assert and
assertion check gets removed in release build which effectively made
the code of closing the regular tab non-existent in release build.

TabModelImpl#closeTab returns a boolean indicating whether the tab
was found which is ambiguous on whether the tab was closed. Hence the
assertion on "found the tab" may be misleading for "closed the tab".

Bug: 1132000

Change-Id: I15eba93453a58beaa32770017545f045b5b310e4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2435085Reviewed-by: Alice Wang <aliceywang@chromium.org>
Commit-Queue: Rohit Agarwal <roagarwal@chromium.org>
Cr-Commit-Position: refs/heads/master@{#811198}

chrome/android/java/src/org/chromium/chrome/browser/incognito/interstitial/IncognitoInterstitialDelegate.java

@@ -73,6 +73,6 @@ public class IncognitoInterstitialDelegate {
         Tab currentRegularTab = TabModelUtils.getCurrentTab(mRegularTabModel);
         mIncognitoTabCreator.launchUrl(
                 currentRegularTab.getUrlString(), TabLaunchType.FROM_CHROME_UI);
-        assert mRegularTabModel.closeTab(currentRegularTab);
+        mRegularTabModel.closeTab(currentRegularTab);
     }
 }
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