target/riscv: rvv: Remove redudant SEW checking for vector fp narrow/widen instructions

target/riscv: rvv: Remove redudant SEW checking for vector fp narrow/widen instructions

If the checking functions check both the single and double width
operators at the same time, then the single width operator checking
functions (require_rvf[min]) will check whether the SEW is 8.

Signed-off-by: Max Chou <max.chou@sifive.com>
Reviewed-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Cc: qemu-stable <qemu-stable@nongnu.org>
Message-ID: <20240322092600.1198921-5-max.chou@sifive.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>