openisa_rv32m1: kconfig: Remove base address/size symbols

RISCV_RV32M1_VECTOR_BASE_ADDR is unused after commit 34b05164
("boards: riscv32: rv32m1_vega: enable MCUboot for ri5cy core") (it was
called RISCV32_RV32M1_BASE_ADDR then).

RISCV_RV32M1_VECTOR_SIZE is still used, but is always 0x100, so remove
it too.

These symbols were only defined in a Kconfig.defconfig file.

Signed-off-by: Ulf Magnusson <Ulf.Magnusson@nordicsemi.no>