[Improvement] Removed redundant validation in PolicyEntity.validate

[justinmclean]

What would you like to be improved?

In core/src/main/java/org/apache/gravitino/meta/PolicyEntity.java, both validatePolicy() and content().validate() are called. validatePolicy() allready calls content().validate().

How should we improve?

Remove the redundant content().validate().

[Jackeyzhe]

@justinmclean Hi, I'd like to work on it. can you assign it to me ?

[justinmclean]

It's yours. If you have any questions, please ask.