target/riscv: Remove redundant declaration pragmas

target/riscv: Remove redundant declaration pragmas

These are now generated by decodetree itself.

Tested-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Acked-by: Palmer Dabbelt <palmer@sifive.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>