[khmer] Drop some more grammar

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

@@ -60,7 +60,7 @@ 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_or_matra_group = (halant_group | matra_group{0,4}) (Coeng (cn|V))?;
+halant_or_matra_group = (matra_group{0,4}) (Coeng (cn|V))?;
 
 
 consonant_syllable =	(c|V|PLACEHOLDER|DOTTEDCIRCLE).n? (halant_group.cn){0,4} halant_or_matra_group syllable_tail;