release 5.4.10

fix deletion dropping in intra-L0

Summary:
`KeyNotExistsBeyondOutputLevel` didn't consider L0 files' key-ranges. So if a key only was covered by older L0 files' key-ranges, we would incorrectly drop deletions of that key. This PR just skips the deletion-dropping optimization when output level is L0.
Closes https://github.com/facebook/rocksdb/pull/2726

Differential Revision: D5617286

Pulled By: ajkr

fbshipit-source-id: 4bff1396b06d49a828ba4542f249191052915bce

Bump up version to 5.4.9

Update headers for more files.

Update java/rocksjni.pom

Some more files.

Remove some left-over BSD headers

Add back the LevelDB license file

Summary: Closes https://github.com/facebook/rocksdb/pull/2591

Differential Revision: D5432696

Pulled By: siying

fbshipit-source-id: a613230ab916de0b279a65ef429ede65460a8db2

Remove the licensing description in CONTRIBUTING.md

Summary: Closes https://github.com/facebook/rocksdb/pull/2590

Differential Revision: D5432539

Pulled By: siying

fbshipit-source-id: 49902453bba3c95c1fb8354441b2198649e52bf4

Change RocksDB License

Summary: Closes https://github.com/facebook/rocksdb/pull/2589

Differential Revision: D5431502

Pulled By: siying

fbshipit-source-id: 8ebf8c87883daa9daa54b2303d11ce01ab1f6f75