x86: kprobes: Remove unused macro stack_addr

An unused macro reported by [-Wunused-macros].

This macro is used to access the sp in pt_regs because at that time
x86_32 can only get sp by kernel_stack_pointer(regs).

'3c88c692 ("x86/stackframe/32: Provide consistent pt_regs")'
This commit have unified the pt_regs and from them we can get sp from
pt_regs with regs->sp easily. Nowhere is using this macro anymore.

Refrencing pt_regs directly is more clear. Remove this macro for
code cleaning.

Link: https://lkml.kernel.org/r/20220924072629.104759-1-chenzhongjin@huawei.com



Signed-off-by: Chen Zhongjin <chenzhongjin@huawei.com>
Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>