tcl: target: imx5{1,3}: remove bogus tapenable command

This seems to be a leftover from borrowing from omap3* configs. Since
SJC is not enabling or disabling the DAP tap, and the tap is always
available, the extra tapenable command causes warnings on startup
(can't enable what's already enabled).

Change-Id: I7514436d565aa5b91876dbdab547956f36dcab77
Signed-off-by: Paul Fertser <fercerpav@gmail.com>
Reviewed-on: http://openocd.zylin.com/3892
Tested-by: jenkins