fix: incorrect base class for exceptions

All exceptions by Shield should implement BaseException.

Author: kenjis

src/Exceptions/SecurityException.php

@@ -4,8 +4,6 @@
 
 namespace CodeIgniter\Shield\Exceptions;
 
-use RuntimeException;
-
 class SecurityException extends RuntimeException
 {
 }

src/Exceptions/ValidationException.php

@@ -4,8 +4,6 @@
 
 namespace CodeIgniter\Shield\Exceptions;
 
-use RuntimeException;
-
 class ValidationException extends RuntimeException
 {
 }