[libfsimage/zfs] compilation fix ZFS libfsimage support.

[libfsimage/zfs] compilation fix ZFS libfsimage support.

Depending on environments, zfs libfsimage support doesn't compile.
This patch fixes it.

ia64-linux-gnu-gcc  -DPIC -O2 -fomit-frame-pointer
-fno-strict-aliasing -std=gnu99 -Wall -Wstrict-prototypes
-Wno-unused-value -Wdeclaration-after-statement
-I/usr/ia64-linux-gnu/
sys-root/usr/include -D__XEN_TOOLS__  -D_LARGEFILE_SOURCE
-D_LARGEFILE64_SOURCE  -I../../../tools/libfsimage/common/ -Werror
-Wp,-MD,.zfs_lzjb.opic.d -fPIC -c -o zfs_lzjb.opic zfs_
lzjb.c
In file included from fsys_zfs.h:41,
                 from zfs_lzjb.c:25:
zfs-include/zfs_acl.h:29: error: redefinition of typedef uid_t
/usr/ia64-linux-gnu/sys-root/usr/include/sys/types.h:82: error:
previous declaration of uid_t was here

This depends on how __uid_t is defined in the system header.
No file under the zfs directory uses uid_t so that just removing
the definition in the zfs_acl.h looks reasonable.

Signed-off-by: Isaku Yamahata <yamahata@valinux.co.jp>