[khmer] Drop some more

src/hb-ot-shape-complex-khmer-machine.rl

@@ -59,7 +59,7 @@ z = ZWJ|ZWNJ;			# is_joiner
 cn = c.ZWJ?.n?;
 matra_group = z{0,3}.M.N?.Coeng?;
 syllable_tail = (z?.SM.SM?.ZWNJ?)? A{0,3}?;
-halant_group = (z?.Coeng.(ZWJ.N?)?);
+halant_group = Coeng;
 halant_or_matra_group = (matra_group{0,4}) (Coeng (cn|V))?;