Make RocksDB build reproducible

Make RocksDB build reproducible

The RocksDB binary included a string with the build timestamp:
> rocksdb_build_git_date:@2021-05-23-16:04:38@

As this changes from build to build, it makes the builds unreproducible.
Simply removing it solves the issue.

This temporary fix can be removed when a proper fix already done in upstream
lands in MariaDB when the RocksDB submodule is updated to a newer release.

Origin: https://github.com/facebook/rocksdb/commit/0a9a05ae12943b1529ef1eabbca5ce5a71c986bf
Bug: https://github.com/facebook/rocksdb/issues/7035
# Merged in RocksDB 6.19.3, but not updated into MariaDB yet

Gbp-Pq: Name fix-reproducible-builds-rocksdb.patch