riscv: Remove obsolete rv32_defconfig file

This file is not used since commit 72f045d ("riscv: Fixup
difference with defconfig"), where it was replaced by the
32-bit.config fragment. Delete the old file to avoid any confusion.

Signed-off-by: Samuel Holland <[email protected]>
Reviewed-by: Conor Dooley <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Palmer Dabbelt <[email protected]>

Author: SiFiveHolland