Revert "x86-64, modify_ldt: Make support for 16-bit segments a runtime option"

commit 7ed6fb9b upstream.

This reverts commit fa81511b in
preparation of merging in the proper fix (espfix64).

Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>