Disable sanitizers (#1456)

Author: paulb777

Example/Firebase.xcodeproj/xcshareddata/xcschemes/AllUnitTests_iOS.xcscheme

@@ -110,8 +110,7 @@
       buildConfiguration = "Debug"
       selectedDebuggerIdentifier = "Xcode.DebuggerFoundation.Debugger.LLDB"
       selectedLauncherIdentifier = "Xcode.DebuggerFoundation.Launcher.LLDB"
-      enableThreadSanitizer = "YES"
-      enableUBSanitizer = "YES"
+      disableMainThreadChecker = "YES"
       shouldUseLaunchSchemeArgsEnv = "YES">
       <Testables>
          <TestableReference
@@ -185,11 +184,6 @@
          </BuildableReference>
       </MacroExpansion>
       <AdditionalOptions>
-         <AdditionalOption
-            key = "NSZombieEnabled"
-            value = "YES"
-            isEnabled = "YES">
-         </AdditionalOption>
       </AdditionalOptions>
    </TestAction>
    <LaunchAction