x86/cpu: Remove "nosep"

That chicken bit was added by

  4f886511 ("[PATCH] i386: allow disabling X86_FEATURE_SEP at boot")

but measuring int80 vsyscall performance on 32-bit doesn't matter
anymore.

If still needed, one can boot with

  clearcpuid=sep

to disable that feature for testing.

Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20220127115626.14179-3-bp@alien8.de