canbus: canopen: Fix broken CANOPEN_STORAGE_HANDLER_ERASES_EEPROM ref.

Missing CONFIG_ prefix in #ifdef, leading to some dead code.

Found by scripts/kconfig/lint.py, which flagged it as unused.

Piggyback removal of a redundant 'default n'.

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