bzip2: Get rid of the custom builder.sh.

Everything the builder.sh did can be done with the generic builder which
makes it easier to override attributes and also easier to read.

The reason I've done this is because of #10820, which tries to override
the preBuild hook, but the latter is hardcoded in the builder.sh of
bzip2.

I have compared the output of this against the previous version and the
only things that were different were timestamps in libbz2.a.

Signed-off-by: aszlig <aszlig@redmoonstudios.org>