config: remove HAVE_KVMALLOC

Sponsored-by: https://despairlabs.com/sponsor/
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Tony Hutter <hutter2@llnl.gov>
Reviewed-by: Tino Reichardt <milky-zfs@mcmilk.de>
Signed-off-by: Rob Norris <robn@despairlabs.com>
Closes #16479

module/os/linux/spl/spl-kmem.c

@@ -134,7 +134,6 @@ EXPORT_SYMBOL(kmem_strfree);
 void *
 spl_kvmalloc(size_t size, gfp_t lflags)
 {
-#ifdef HAVE_KVMALLOC
 	/*
 	 * GFP_KERNEL allocations can safely use kvmalloc which may
 	 * improve performance by avoiding a) high latency caused by
@@ -146,7 +145,6 @@ spl_kvmalloc(size_t size, gfp_t lflags)
 	 */
 	if ((lflags & GFP_KERNEL) == GFP_KERNEL)
 		return (kvmalloc(size, lflags));
-#endif
 
 	gfp_t kmalloc_lflags = lflags;