Revert unnecessary zlib_inflate/inftrees.c fix

It turns out that empty distance code tables are not an error, and that
a compressed block with only literals can validly have an empty table
and should not be flagged as a data error.

Some old versions of gzip had problems with this case, but it does not
affect the zlib code in the kernel.

Analysis and explanations thanks to Sergey Vlasov <vsu@altlinux.ru>

Signed-off-by: Linus Torvalds <torvalds@osdl.org>