riscv: drop cpufeature_apply_feature tracking variable

The variable was tracking which feature patches got applied
but that information was never actually used - and thus resulted
in a warning as well.

Drop the variable.

Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Reviewed-by: Guo Ren <guoren@kernel.org>
Link: https://lore.kernel.org/r/20220526205646.258337-2-heiko@sntech.de
Fixes: ff689fd2

 ("riscv: add RISC-V Svpbmt extension support")
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>