Revert "Make inserts use COMPAT_1416 for now (** MUST REVERT IN 1467 **)"

This reverts commit 6df665c5a9a269fd9882e6de391782e871b598d1.
Centralise choice of default compatibility mode
Set default compatibility mode to COMPAT_1416 until after 1466 has shipped (*** FIXME MUST REVERT ***)