x86/stacktrace: Remove STACKTRACE_DUMP_ONCE

x86/stacktrace: Remove STACKTRACE_DUMP_ONCE

The stack unwinding can sometimes fail yet. Especially with the
generated debug info. So do not yell at users -- live patching (the only
user of this interface) will inform the user about the failure
gracefully.

And given this was the only user of the macro, remove the macro proper
too.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/lkml/20180518064713.26440-2-jslaby@suse.cz
Signed-off-by: Ingo Molnar <mingo@kernel.org>