Summary:
The current blob db implementation use mix of int32_t, uint32_t and uint64_t for TTL and expiration. Update all timestamps to uint64_t for consistency.
Closes https://github.com/facebook/rocksdb/pull/2683
Differential Revision: D5557103
Pulled By: yiwu-arbug
fbshipit-source-id: e4eab2691629a755e614e8cf1eed9c3a681d0c42