Remove unused iov_iter_init_compat() wrapper

This compatibility code is no longer needed.  For it a while
iov_iter_init_compat() was used by zfs_uio_prefaultpages() but
this code should have been dropped as part of commit 83b91ae.
Take care of that oversight and remove it.

Reviewed-by: Brian Atkinson <batkinson@lanl.gov>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #11543

config/kernel-vfs-iov_iter.m4

@@ -10,31 +10,6 @@ AC_DEFUN([ZFS_AC_KERNEL_SRC_VFS_IOV_ITER], [
 		    ITER_IOVEC | ITER_KVEC | ITER_BVEC | ITER_PIPE;
 	])
 
-	ZFS_LINUX_TEST_SRC([iov_iter_init], [
-		#include <linux/fs.h>
-		#include <linux/uio.h>
-	],[
-		struct iov_iter iter = { 0 };
-		struct iovec iov;
-		unsigned long nr_segs = 1;
-		size_t count = 1024;
-
-		iov_iter_init(&iter, WRITE, &iov, nr_segs, count);
-	])
-
-	ZFS_LINUX_TEST_SRC([iov_iter_init_legacy], [
-		#include <linux/fs.h>
-		#include <linux/uio.h>
-	],[
-		struct iov_iter iter = { 0 };
-		struct iovec iov;
-		unsigned long nr_segs = 1;
-		size_t count = 1024;
-		size_t written = 0;
-
-		iov_iter_init(&iter, &iov, nr_segs, count, written);
-	])
-
 	ZFS_LINUX_TEST_SRC([iov_iter_advance], [
 		#include <linux/fs.h>
 		#include <linux/uio.h>
@@ -114,25 +89,6 @@ AC_DEFUN([ZFS_AC_KERNEL_VFS_IOV_ITER], [
 		enable_vfs_iov_iter="no"
 	])
 
-	dnl #
-	dnl # 'iov_iter_init' available in Linux 3.16 and newer.
-	dnl # 'iov_iter_init_legacy' available in Linux 3.15 and older.
-	dnl #
-	AC_MSG_CHECKING([whether iov_iter_init() is available])
-	ZFS_LINUX_TEST_RESULT([iov_iter_init], [
-		AC_MSG_RESULT(yes)
-		AC_DEFINE(HAVE_IOV_ITER_INIT, 1,
-		    [iov_iter_init() is available])
-	],[
-		ZFS_LINUX_TEST_RESULT([iov_iter_init_legacy], [
-			AC_MSG_RESULT(yes)
-			AC_DEFINE(HAVE_IOV_ITER_INIT_LEGACY, 1,
-			    [iov_iter_init() is available])
-		],[
-			ZFS_LINUX_TEST_ERROR([iov_iter_init()])
-		])
-	])
-
 	AC_MSG_CHECKING([whether iov_iter_advance() is available])
 	ZFS_LINUX_TEST_RESULT([iov_iter_advance], [
 		AC_MSG_RESULT(yes)

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

@@ -111,19 +111,6 @@ zfs_uio_index_at_offset(zfs_uio_t *uio, offset_t off, uint_t *vec_idx)
 	return (off);
 }
 
-static inline void
-iov_iter_init_compat(struct iov_iter *iter, unsigned int dir,
-    const struct iovec *iov, unsigned long nr_segs, size_t count)
-{
-#if defined(HAVE_IOV_ITER_INIT)
-	iov_iter_init(iter, dir, iov, nr_segs, count);
-#elif defined(HAVE_IOV_ITER_INIT_LEGACY)
-	iov_iter_init(iter, iov, nr_segs, count, 0);
-#else
-#error "Unsupported kernel"
-#endif
-}
-
 static inline void
 zfs_uio_iovec_init(zfs_uio_t *uio, const struct iovec *iov,
     unsigned long nr_segs, offset_t offset, zfs_uio_seg_t seg, ssize_t resid,