swift234

Revert "Summon the eldritch horror "EagerDeserializationDecls" from the bowels of history."

This reverts commit dc98e17d84b991b6be8b8feb5e0d05aad24f52a4.

I believe this commit was causing test failures on:
  IRGen/c_layout.sil
  IRGen/existentials.sil
It also recreates the file lib/Serialization/ModuleFormat.h,
which really can't have been intended.

Swift SVN r23732