Since commit f0bddf50 ("riscv: entry: Convert to generic entry"),
_TIF_WORK_MASK is no longer used, so remove it.

Fixes: f0bddf50 ("riscv: entry: Convert to generic entry")
Signed-off-by: Jinjie Ruan <ruanjinjie@huawei.com>
Reviewed-by: Guo Ren <guoren@kernel.org>
Reviewed-by: Andy Chiu <andy.chiu@sifive.com>
Link: https://lore.kernel.org/r/20240711111508.1373322-1-ruanjinjie@huawei.comSigned-off-by: Palmer Dabbelt <palmer@rivosinc.com>