target: remove unused codes from enum tcm_tmrsp_table

Three have been checked for but were never set.  Remove the dead code.
Also renumbers the remaining ones to a) get rid of the holes after the
removal and b) avoid a collision between TMR_FUNCTION_COMPLETE==0 and
the uninitialized case.  If we failed to set a code, we should rather
fall into the default case then return success.

Signed-off-by: Joern Engel <joern@logfs.org>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>