Fix egregious typo in cmpTypeX
Reported in Trac #7272. "tv1" should be "tv2"! However, things weren't as simple as they sound, because treating (x:Open) as different from (x:*) gave rise to new failures; see Note [Comparison with OpenTypeKind] in Type. My hacky solution is to treat OpenKind as equal to * and #, at least in Core etc. Hence the faff in Type.cmpTc. I do not like this. But it seems like another messy consequence of including sub-kinding. Sigh.