avr32: init cannot ignore signals sent by force_sig_info()

avr32: init cannot ignore signals sent by force_sig_info()

We can delete the code that checks to see if we're sending an ignored
signal to init because force_sig_info() already handles this case.
force_sig_info() will kill init even if the signal handler is SIG_DFL
and the scenario described in the comment where init might "generate
the same exception over and over again" cannot occur (force_sig_info()
clears SIGNAL_UNKILLABLE to ensure that init will die).

Also, the use of is_global_init() is not correct in the multhreaded
case, as Oleg Nesterov explains,

	"is_global_init() is not right in theory, /sbin/init can be
	multithreaded. And, this doesn't cover the sub-namespace
	inits... I'd suggest to check SIGNAL_UNKILLABLE, but looking
	closer I think you can simply remove this code."

It seems this code was copied from arch/powerpc in March 2007 in commit

  623b0355d5b1 "[AVR32] Clean up exception handling code"

but the code was deleted from arch/powerpc in November 2009 in commit

  a0592d42fe3e "powerpc: kill the obsolete code under is_global_init()"

So catch up with powerpc and delete the bogus code.

Signed-off-by: Matt Fleming <matt.fleming@linux.intel.com>
Signed-off-by: Hans-Christian Egtvedt <hans-christian.egtvedt@atmel.com>