[RFC PATCH] treewide: remove bzip2 compression support

[Alex Xu (Hello71)]

Excerpts from Alex Xu (Hello71)'s message of December 15, 2020 2:03 pm:
> bzip2 is either slower or larger than every other supported algorithm,
> according to benchmarks at [0]. It is far slower to decompress than any
> other algorithm, and still larger than lzma, xz, and zstd.
> 
> [0] https://lore.kernel.org/lkml/1588791882.08g1378g67.none@localhost/
> 
> Signed-off-by: Alex Xu (Hello71) <alex_y_xu at yahoo.ca>

Upon further research, I found that bzip2 removal was already 
implemented as part of zstd addition, but were apparently abandoned in 
an effort to get zstd in. I will check those patches and try sending 
those instead. Thanks to all reviewers for comments on this patch.