[BUG]: McStas Al_window only applies absorption xs

[willend]

Describe the bug
DIKU MSc studen Torben G Hansen has spotted that the 4th-order pol calculation in \lambda in lines 83-85 resulting in value Al_my_tot is actually unused

McCode/mcstas-comps/contrib/Al_window.comp

Line 85 in 0b57bc4

Al_my_tot = Al_rho / Al_mmol * Al_s_tot_lambda * avogadro * 10;

(p does not depend on the value

McCode/mcstas-comps/contrib/Al_window.comp

Line 88 in 0b57bc4

p *= exp (-Al_my_a * dist); /* neutron passes window without any interaction */

)