Fix two undocumented parameters to functions from ENR patch.

On ProcessUtility document the parameter, to match others.

On CreateCachedPlan drop the queryEnv parameter.  It was not
referenced within the function, and had been added on the
assumption that with some unknown future usage of QueryEnvironment
it might be useful to do something there.  We have avoided other
"just in case" implementation of unused paramters, so drop it here.

Per gripe from Tom Lane