[RISCV] Remove required features zvfhmin/zvfbfmin from plain f16/bf16 intrinsics (llvm#145891)

We've checked f16/bf16 vector type support using `checkRVVTypeSupport`.
So it's not necessary to add the required features for plain f16/bf16
intrinsics that do not use actual instructions from zvfhmin/zvfbfmin.

Author: tclin914