boards: nucleo_wb55cg: Set partition for swap f/w update method

Flash partition was defining a scratch area which was implying the use
of mcuboot BOOT_SWAP_USING_SCRATCH f/w update method.
By removing this partition, mcuboot will automatically use
BOOT_PREFER_SWAP_MOVE method which should be prefered as it levels
flash wear. Incidentally increase slot1 by one sector (as this is
preferred for the swap method).

Signed-off-by: Erwan Gouriou <erwan.gouriou@st.com>
1 file changed