Fix leak in S3 VFS read (#2189)
Fix leak in S3 VFS read (#2189)

This fix a leak in the S3 read code path where we allocated a
`boost::interprocess::bufferbuf` but did not free it. This changes from
a raw pointer to a std::unique_ptr.
TileDB-Inc/TileDB,TileDB-Inc/TileDB,TileDB-Inc/TileDB,TileDB-Inc/TileDB