sh: remove EXPEVT vector from stack on sh3/sh4/sh4a

Remove EXPEVT vector from the stack, lookup_exception_vector()
for sh3/sh4/sh4a is already using k2 to get the vector.

Signed-off-by: Magnus Damm <damm@igel.co.jp>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>