riscv/vdso: Drop unneeded part due to merge issue

It seems that something is wrong when patch "riscv/vdso:
Refactor asm/vdso.h" is merged.

Let's fix the merge issue.

Fixes: 8edab023 ("Merge remote-tracking branch 'palmer/riscv-vdso-cleanup' into for-next")
Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>