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 should be

    idFound = top->getValue(name, ret);

it might be cleaner to say

    if (top->getValue()).. return ret;

and break out of the loop if getValue returns true;  But either style is fine.

The loop would be clearer assigning lexer = parentLex before it, and updating lexer after the getValue()