proc: Remove kernel stack swapping support, part 9

[markj]

Summary

setrunnable() no longer needs to return a value. Make its return type
void and fix up callers. Now a number of other interfaces no longer
need to return a value, they will be fixed up subsequently.

[kib]

sys/kern/kern_sig.c

2399

just return;?
same for all other goto out places.

sys/kern/subr_sleepqueue.c

973

[markj]

Simplify return value handling in tdsendsignal().