tests: don't duplicate mnt_enablefs entry

this avoids:

===================== Run zdtm/static/socket-tcpbuf6 in h ======================
Makefile:295: target 'mnt_enablefs.pid' given more than once in the same rule
Start test
Makefile:295: target 'mnt_enablefs.pid' given more than once in the same rule
./socket-tcpbuf6 --pidfile=socket-tcpbuf6.pid --outfile=socket-tcpbuf6.out
Run criu dump
Run criu restore
Wait for zdtm/static/socket-tcpbuf6 to die for 0.100000
Wait for zdtm/static/socket-tcpbuf6 to die for 0.200000
Removing dump/zdtm/static/socket-tcpbuf6/27
===================== Test zdtm/static/socket-tcpbuf6 PASS =====================

in every test.
Signed-off-by: Tycho Andersen <tycho.andersen@canonical.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>

test/zdtm/static/Makefile

@@ -244,7 +244,6 @@ TST_DIR		=				\
 		unlink_regular00		\
 		mnt_enablefs			\
 		autofs				\
-		mnt_enablefs			\
 
 TST_DIR_FILE	=				\
 		chroot				\