Delete unused method

Author: sebastianbergmann

src/Framework/TestCase.php

@@ -926,14 +926,6 @@ final public function setInIsolation(bool $inIsolation): void
         $this->inIsolation = $inIsolation;
     }
 
-    /**
-     * @internal This method is not covered by the backward compatibility promise for PHPUnit
-     */
-    final public function isInIsolation(): bool
-    {
-        return $this->inIsolation;
-    }
-
     /**
      * @internal This method is not covered by the backward compatibility promise for PHPUnit
      */