McXtrace 3.0: Single_crystal and PowderN can not coexist in same instrument

[willend]

The components have different structs with same name.

Fixed on mccode-3 and mcxtrace-3.0-release branches: https://github.com/McStasMcXtrace/McCode/commit/879e854b29c2adfb5bae63e816446e0a78ccc9ba

If needed, update your local Single_crystal by this one: Single_crystal.comp.txt (https://github.com/McStasMcXtrace/McCode/blob/mccode-3/mcxtrace-comps/samples/PowderN.comp)