linker: Remove deprecated Kconfig options related to linker scripts

Remove Kconfig, linker script, and related bits associated with
CUSTOM_RODATA_LD, CUSTOM_RWDATA_LD, CUSTOM_SECTIONS_LD,
SOC_NOINIT_LD, SOC_RODATA_LD, and SOC_RWDATA_LD options that have been
deprecated since Zephyr 2.2.

Signed-off-by: Kumar Gala <kumar.gala@linaro.org>