config: remove HAVE_KTIME_GET_RAW_TS64

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 openzfs#16479

config/kernel.m4

@@ -104,7 +104,6 @@ AC_DEFUN([ZFS_AC_KERNEL_TEST_SRC], [
 	ZFS_AC_KERNEL_SRC_KUID_HELPERS
 	ZFS_AC_KERNEL_SRC_RENAME
 	ZFS_AC_KERNEL_SRC_USERNS_CAPABILITIES
-	ZFS_AC_KERNEL_SRC_KTIME
 	ZFS_AC_KERNEL_SRC_TOTALRAM_PAGES_FUNC
 	ZFS_AC_KERNEL_SRC_TOTALHIGH_PAGES
 	ZFS_AC_KERNEL_SRC_PERCPU
@@ -221,7 +220,6 @@ AC_DEFUN([ZFS_AC_KERNEL_TEST_RESULT], [
 	ZFS_AC_KERNEL_KUID_HELPERS
 	ZFS_AC_KERNEL_RENAME
 	ZFS_AC_KERNEL_USERNS_CAPABILITIES
-	ZFS_AC_KERNEL_KTIME
 	ZFS_AC_KERNEL_TOTALRAM_PAGES_FUNC
 	ZFS_AC_KERNEL_TOTALHIGH_PAGES
 	ZFS_AC_KERNEL_PERCPU

include/os/linux/spl/sys/time.h

@@ -81,13 +81,8 @@ gethrestime_sec(void)
 static inline hrtime_t
 gethrtime(void)
 {
-#if defined(HAVE_KTIME_GET_RAW_TS64)
 	struct timespec64 ts;
 	ktime_get_raw_ts64(&ts);
-#else
-	struct timespec ts;
-	getrawmonotonic(&ts);
-#endif
 	return (((hrtime_t)ts.tv_sec * NSEC_PER_SEC) + ts.tv_nsec);
 }