Move package javadoc to package-info,

drop overview which is the same as description for jakarta.mail package

Signed-off-by: Lukas Jungmann <lukas.jungmann@oracle.com>

api/src/main/java/jakarta/mail/event/package-info.java

@@ -0,0 +1,22 @@
+/*
+ * Copyright (c) 2021 Oracle and/or its affiliates. All rights reserved.
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Public License v. 2.0, which is available at
+ * http://www.eclipse.org/legal/epl-2.0.
+ *
+ * This Source Code may also be made available under the following Secondary
+ * Licenses when the conditions for such availability set forth in the
+ * Eclipse Public License v. 2.0 are satisfied: GNU General Public License,
+ * version 2 with the GNU Classpath Exception, which is available at
+ * https://www.gnu.org/software/classpath/license.html.
+ *
+ * SPDX-License-Identifier: EPL-2.0 OR GPL-2.0 WITH Classpath-exception-2.0
+ */
+
+/**
+ * Listeners and events for the Jakarta Mail API.
+ * This package defines listener classes and event classes used by the classes
+ * defined in the <code>jakarta.mail</code> package.
+ */
+package jakarta.mail.event;