Change well-formedness check to allow for toplevel `ref` memories

[nathanielnrn]

As part of #1932 and #1733 we probably want to allow toplevel modules to contain ref memories and still be considered wellformed. Perhaps only if we designate that we wish to compile for synthesis/AXI wrapped. Not sure where this well-formed check lives as of writing.

[sampsyo]

The check lives here!

calyx/calyx-opt/src/passes/well_formed.rs

Lines 99 to 109 in f52e552

	// Main component cannot use `ref` cells
	if comp.name == ctx.entrypoint {
	for cell in comp.cells.iter() {
	if cell.borrow().is_reference() {
	return Err(Error::malformed_structure(
	"ref cells are not allowed for main component",
	)
	.with_pos(cell.borrow().get_attributes()));
	}
	}
	}

I say we can just delete this. No fuss, no muss.

[nathanielnrn]

Closed via #1952