Remove adaptive mutex implementation

Since the Linux 2.6.29 kernel all mutexes have been adaptive mutexs.
There is no longer any point in keeping this code so it is being
removed to simplify the code.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>

config/spl-build.m4

@@ -28,7 +28,6 @@ AC_DEFUN([SPL_AC_CONFIG_KERNEL], [
 	SPL_AC_TYPE_UINTPTR_T
 	SPL_AC_2ARGS_REGISTER_SYSCTL
 	SPL_AC_SHRINKER_CALLBACK
-	SPL_AC_TASK_CURR
 	SPL_AC_CTL_UNNUMBERED
 	SPL_AC_CTL_NAME
 	SPL_AC_VMALLOC_INFO
@@ -997,23 +996,6 @@ AC_DEFUN([SPL_AC_SHRINKER_CALLBACK],[
 	EXTRA_KCFLAGS="$tmp_flags"
 ])
 
-dnl #
-dnl # Custom SPL patch may export this system it is not required
-dnl #
-AC_DEFUN([SPL_AC_TASK_CURR],
-	[AC_MSG_CHECKING([whether task_curr() is available])
-	SPL_LINUX_TRY_COMPILE_SYMBOL([
-		#include <linux/sched.h>
-	], [
-		task_curr(NULL);
-	], [task_curr], [kernel/sched.c], [
-		AC_MSG_RESULT(yes)
-		AC_DEFINE(HAVE_TASK_CURR, 1, [task_curr() is available])
-	], [
-		AC_MSG_RESULT(no)
-	])
-])
-
 dnl #
 dnl # 2.6.19 API change,
 dnl # Use CTL_UNNUMBERED when binary sysctl is not required
@@ -1220,7 +1202,9 @@ AC_DEFUN([SPL_AC_INODE_I_MUTEX], [
 
 dnl #
 dnl # 2.6.29 API change,
-dnl # Adaptive mutexs introduced.
+dnl # Adaptive mutexs were introduced which track the mutex owner.  The
+dnl # mutex wrappers leverage this functionality to avoid tracking the
+dnl # owner multipe times.
 dnl #
 AC_DEFUN([SPL_AC_MUTEX_OWNER], [
 	AC_MSG_CHECKING([whether struct mutex has owner])