Revert "print kernel stacktrace for exceptions in kernel"

This reverts commit eff1369cab.

This was in a working branch and I only intended to commit
exception.c. But I committed the exact inverse. Sorry.

kernel/system/do_sigreturn.c

@@ -56,10 +56,8 @@ PUBLIC int do_sigreturn(struct proc * caller, message * m_ptr)
 #if (_MINIX_CHIP == _CHIP_INTEL)
   if(sc.sc_flags & MF_FPU_INITIALIZED)
   {
-	fpu_verifychecksum(rp);
 	memcpy(rp->p_fpu_state.fpu_save_area_p, &sc.sc_fpu_state,
 		FPU_XFP_SIZE);
-	fpu_makechecksum(rp);
 	rp->p_misc_flags |=  MF_FPU_INITIALIZED; /* Restore math usage flag. */
 	/* force reloading FPU */
 	release_fpu(rp);