x86/lguest: Remove lguest support

Lguest seems to be rather unused these days. It has seen only patches
ensuring it still builds the last two years and its official state is
"Odd Fixes".

Remove it in order to be able to clean up the paravirt code.

Signed-off-by: Juergen Gross <jgross@suse.com>
Acked-by: Rusty Russell <rusty@rustcorp.com.au>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: boris.ostrovsky@oracle.com
Cc: lguest@lists.ozlabs.org
Cc: rusty@rustcorp.com.au
Cc: xen-devel@lists.xenproject.org
Link: http://lkml.kernel.org/r/20170816173157.8633-3-jgross@suse.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/include/uapi/asm/bootparam.h

@@ -201,7 +201,7 @@ struct boot_params {
  *
  * @X86_SUBARCH_PC: Should be used if the hardware is enumerable using standard
  *	PC mechanisms (PCI, ACPI) and doesn't need a special boot flow.
- * @X86_SUBARCH_LGUEST: Used for x86 hypervisor demo, lguest
+ * @X86_SUBARCH_LGUEST: Used for x86 hypervisor demo, lguest, deprecated
  * @X86_SUBARCH_XEN: Used for Xen guest types which follow the PV boot path,
  * 	which start at asm startup_xen() entry point and later jump to the C
  * 	xen_start_kernel() entry point. Both domU and dom0 type of guests are