swift234

For unsafeReferenceCast rely on static verifier checks.

The debugAsserts were nicely self-documenting, but generate an obscene
amount of useless SIL code that is inlined everywhere and sticks around
when we compile the stdlib. The old asserts would need to be fixed to
support Optionals but that makes the situation much worse.

Why is it ok to remove the asserts?
_unsafeReferenceCast remains an internal API. The invariants are checked
statically whenever the routine is specialized, and dynamically checked
by the runtime cast.

Swift SVN r32795