Revert "boot: Enable MCUBOOT_DEV_WITH_ERASE in other systems"

Need to revert changes provided to support devices without erase
until problme with TF-M, missing implementation of flash_area_get_sector,
is resolved.

This reverts commit e5c0078f.

Signed-off-by: Dominik Ermel <dominik.ermel@nordicsemi.no>