TimingTest: remove flaky assertions

This should probably get a better test to ensure that the method actually returns microseconds, but time is difficult to test, which makes these assertions flaky and that's even worse.

For now, let's remove the flaky assertions.

Author: jrfnl

tests/Core/Util/Timing/TimingTest.php

@@ -52,8 +52,6 @@ public function testGetDurationWithStartReturnsMilliseconds()
         $duration = Timing::getDuration();
 
         $this->assertTrue(is_float($duration));
-        $this->assertGreaterThan(1, $duration);
-        $this->assertLessThan(15, $duration);
 
     }//end testGetDurationWithStartReturnsMilliseconds()