INT-16757: tearDown() fix for unit tests and removed files from phpunit

Author: jgg9026

tests/aws_apcu_cache_test.php

@@ -51,7 +51,7 @@ protected function setUp(): void {
         }
     }
 
-    protected function tearDown() {
+    protected function tearDown(): void {
         apcu_delete(self::TEST_KEY);
     }