xtensa: Remove signal translation and exec_domain

As execution domain support is gone we can remove
signal translation from the signal code and remove
exec_domain from thread_info.

Signed-off-by: Richard Weinberger <richard@nod.at>

diff --cc arch/xtensa/include/asm/thread_info.h
Simple merge

diff --cc arch/xtensa/kernel/signal.c
Simple merge