Replace lz4net with K4os.Compression.LZ4 on net452
Description
In CSHARP-719, we started targeting K4os.Compression.LZ4 for netstandard but we kept lz4net for net452. We should use K4os.Compression.LZ4 for net452 too in the next major.
Users should not be impacted by this whatsoever since this is used internally by the driver and the user doesn't ever interact with lz4 directly through the driver. Furthermore, the driver uses an API of the library that is compatible with the previous one (lz4net).
Environment
None
