thread: remove THREAD_LOCAL_EXCEPTION_SPS

Removes unused THREAD_LOCAL_EXCEPTION_SPS code.

Signed-off-by: Jens Wiklander <jens.wiklander@linaro.org>
Tested-by: Jens Wiklander <jens.wiklander@linaro.org> (QEMU virt platform)
Reviewed-by: Pascal Brand <pascal.brand@linaro.org>
Reviewed-by: Joakim Bech <joakim.bech@linaro.org>