MAINTAINERS: Remove Bin Meng from RISC-V maintainers

MAINTAINERS: Remove Bin Meng from RISC-V maintainers

Bin Meng has been a long time contributor and maintainer for QEMU RISC-V
and has been very beneficial to the RISC-V ecosystem.

Unfortunately his email has started to bounce so this patch is removing
them from MAINTAINERS. If in the future Bin Meng wants to return we will
happily re-add them.

Note that I'm not removing Bin Meng as a "SD (Secure Card)" maintainer.

Signed-off-by: Alistair Francis <alistair.francis@wdc.com>
Acked-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Message-ID: <20250128060546.1374394-1-alistair.francis@wdc.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>