Fix flaky tests ProgrammaticTabModelTest/TabModelTest.*

The tests ProgrammaticTabModelTest/TabModelTest.* tried to
clean up the session file using NSFileManager but this step
was flaky due to a race condition (it sometimes fails with
a permission error).

TestChromeBrowserState already delete the state directory
if no explicit path is passed to the builder, thus the step
to clean up was unnecessary and can be removed.

Bug: none
Change-Id: If0ece62ee5cee726e4135952f3d50efae35dabb6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1865211
Auto-Submit: Sylvain Defresne <sdefresne@chromium.org>
Reviewed-by: Stepan Khapugin <stkhapugin@chromium.org>
Commit-Queue: Sylvain Defresne <sdefresne@chromium.org>
Cr-Commit-Position: refs/heads/master@{#706450}

ios/chrome/browser/tabs/tab_model_unittest.mm

@@ -666,14 +666,9 @@ TEST_P(TabModelTest, RestorePersistedSessionAfterEmpty) {
   [tab_model_ restoreSessionWindow:session_window forInitialRestore:NO];
 
   EXPECT_EQ(0U, [tab_model_ count]);
-  EXPECT_TRUE([[NSFileManager defaultManager] removeItemAtPath:state_path
-                                                         error:nullptr]);
 }
 
 TEST_P(TabModelTest, DISABLED_PersistSelectionChange) {
-  NSString* stashPath =
-      base::SysUTF8ToNSString(chrome_browser_state_->GetStatePath().value());
-
   // Reset the TabModel with a custom SessionServiceIOS (to control whether
   // data is saved to disk).
   TestSessionService* test_session_service = [[TestSessionService alloc] init];
@@ -723,10 +718,6 @@ TEST_P(TabModelTest, DISABLED_PersistSelectionChange) {
 
   EXPECT_EQ(tab_model_.webStateList->GetWebStateAt(1),
             tab_model_.webStateList->GetActiveWebState());
-
-  // Clean up.
-  EXPECT_TRUE([[NSFileManager defaultManager] removeItemAtPath:stashPath
-                                                         error:nullptr]);
 }
 
 INSTANTIATE_TEST_SUITE_P(ProgrammaticTabModelTest,