Framework should not allow the "uuid" attribute to be removed.

The framework should guard against removing the "uuid" attribute. Code already exists to do this, but it appears that a bug exists that does allow the "uuid" attribute to be removed if the removal is done with a regular expression.

I.e., StandardProcessSession.removeAllAttributes(FlowFile, Pattern) does not protected against this, though StandardProcessSession.removeAllAttributes(FlowFile, Set) and StandardProcessSession.removeAttribute(FlowFile, String) do protect against it.

We need to ensure that all attribute removal methods protect against this.