Use "OrCoVar" functions less
This is a step towards #17291.
-
mkLocalId
now asserts that it's not given a covar. - Don't use "OrCoVar" functions where we know the expression is not a coercion. All remaining occurrences of
OrCoVar
are called on a coercion variable during a build. - Remove
dataConSig
, as its use was limited to fetchingdataConOrigResTy
.