jtag: retire jtag_alloc_in_value32

no longer used after arm7/9tdmi.c stopped using it.

Change-Id: I65bfe67641970e63e8276cbd378aa68f5701a8d9
Signed-off-by: Øyvind Harboe <oyvind.harboe@zylin.com>
Reviewed-on: http://openocd.zylin.com/263


Tested-by: jenkins
Reviewed-by: Spencer Oliver <spen@spen-soft.co.uk>