riscv: rely on core code to keep thread_info::cpu updated

mainline inclusion
from mainline-v5.16-rc1
commit 8aa0fb0f
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I4Q94A


CVE: NA

------------------------------

Now that the core code switched back to using thread_info::cpu to keep
a task's CPU number, we no longer need to keep it in sync explicitly. So
just drop the code that does this.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Acked-by: Palmer Dabbelt <palmerdabbelt@google.com>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Guan Jing <guanjing6@huawei.com>
Reviewed-by: Chen Hui <judy.chenhui@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>