We previously build the ESM facade (synthetic modules re-exporting
builtin's exports) for builtins even when they are not directly
import'ed (which rarely happens for internal builtins as that
requires --expose-internals). This patch removes
the eager generation to avoid the overhead and the extra
promises created in facade building when it's not reqested by the user.
When the facade is needed the ESM loader that can be requested
it in the translator on-demand.

Drive-by: set the ModuleWrap prototype to null in the built-in
snapshot.

It is easier to filter the core startup benchmark with this name.