swift234

Revert "[deserialization] Deserialize WitnessTables/VTables in SILModule, not in SILLinking."

This reverts commit r14623. I will recommit this when I reenable deserialization
of witness tables/vtables. This will enable the deserialization of SILFunctions
by default from the stdlib by avoiding the lack of external witness
tables/vtables.

Swift SVN r14786