[temp.constr.expr] Remove constraint equivalence.

To be defined in terms of equivalence. Core issues
deal with namespaces and parentheses.
[temp.constr.expr] Rewrite normalization rules

To be consistent with normalization/normalized.
[various] Be consistent with normalized/normalization.

Define both normalization as the process and normalized
as the a single step in the process.
[temp.constr] Fix typo.

And don't refer to normalization before its defined.
[expr.prim.general] Require constraint checks for
id-expressions referring to constrained functions.