x86: remove old lzma tuning patch

Chen Minqiang reported in his GitHub PR openwrt#4733 that:
With CONFIG_TARGET_INITRAMFS_COMPRESSION_LZMA=y option set,
the popular x86/amd64 target's initramfs-kernel failed to boot.

The cause for this boot failure is that the LZMA compression
uses a the first bytes to encode the compression parameters.
It does not have a fixed magic. Yes, this only works if the
the existing lzma options in the upstream are not changed.

This patch does away with OpenWrt special LZMA options tuning
since it is rather unlikely that upstream will improve the
compression algorithm detection after all this time. Even
though, the tuning produced a smaller initramfs (~1.1% in a
spot check).

Link: <openwrt#4733>
Reported-by: Chen Minqiang <ptpt52@gmail.com>
Signed-off-by: Christian Lamparter <chunkeey@gmail.com>