HPCC-9892 Remove dummy LOADXML

This is a stage1 fix. It allows for dummy LOADXMLs to be removed
and have macro parameters declared before an internal (to macro def) LOADXML
to still exist.

This alters none of the ill behaviours relating to %IDs% and LOADXMLs.

Signed-off-by: jamienoss <james.noss@lexisnexis.com>
This is a change in semantics.  Previously it would only have looked in the current scope.  Now it will look in parent scopes.

It seems a good change, but could it possibly cause any issues.  E.g., if a value is blank in one scope, if will search the parent.  Better would be to finish if getValue() returns true.