Fix ShellMethod not using context validator

(cherry picked from commit 23194d0)

- Backport #493
- Fixes #496

Author: terminalsin

spring-shell-core/src/main/java/org/springframework/shell/command/invocation/InvocableShellMethod.java

@@ -298,7 +298,6 @@ protected Object doInvoke(Object... args) throws Exception {
 		try {
 			if (validator != null) {
 				Method bridgedMethod = getBridgedMethod();
-				Validator validator = Utils.defaultValidator();
 				Set<ConstraintViolation<Object>> constraintViolations = validator.forExecutables()
 						.validateParameters(getBean(), bridgedMethod, args);
 				if (constraintViolations.size() > 0) {