ia64/kprobes: remove orphan declarations from arch/ia64/include/asm/kprobes.h

ia64/kprobes: remove orphan declarations from arch/ia64/include/asm/kprobes.h

flush_register_stack() and invalidate_stacked_regs() have been removed
since commit 0aeaf6b3a345 ("ia64/kprobes: Remove jprobe implementation"),
so remove them.

Link: https://lkml.kernel.org/r/20220914124707.1483471-1-cuigaosheng1@huawei.com
Signed-off-by: Gaosheng Cui <cuigaosheng1@huawei.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>