Remove unnecessary code to cleanup tests

WP test case cleans the database automatically after each test so there is no need to do it automatically.

tests/unit-tests/log/log-handler-db.php

@@ -6,16 +6,6 @@
  * @since 3.0.0
  */
 class WC_Tests_Log_Handler_DB extends WC_Unit_Test_Case {
-	public function setUp() {
-		parent::setUp();
-		WC_Log_Handler_DB::flush();
-	}
-
-	public function tearDown() {
-		WC_Log_Handler_DB::flush();
-		parent::tearDown();
-	}
-
 	/**
 	 * Test handle writes to database correctly.
 	 *