Don't rely on inferior I/O in {call-signal-resume, unwindonsignal}.exp

Don't rely on inferior I/O in {call-signal-resume, unwindonsignal}.exp

These tests rely on inferior I/O, but that seems pointless and
unrelated here.  Simply remove the printf calls, and don't expect
them.

gdb/testsuite/ChangeLog:
2015-07-29  Pedro Alves  <palves@redhat.com>

	* gdb.base/call-signal-resume.exp: Remove check for
	gdb,noinferiorio.  Don't expect "no signal".  Use gdb_test.
	* gdb.base/unwindonsignal.exp: Likewise.
	* gdb.base/call-signals.c (gen_signal): Remove printf call.
	* gdb.base/unwindonsignal.c (gen_signal): Likewise.