Previously, ~raw_hash_set() would change *this to have the same
representation as an empty hash table. This is unnecessary since
nobody should be touching a destroyed hash table, and prevents future
optimizations/changes that might not be able to preserve this
behavior.

PiperOrigin-RevId: 487899950
Change-Id: I2d4470677bdd411c2e48ef511187e39f4e7fc2f4