cr50: drop unused definition of CONFIG_FLASH_READOUT_PROTECTION
cr50: drop unused definition of CONFIG_FLASH_READOUT_PROTECTION

No code depending on this define is relevant for Cr50, it was added to
this board file by mistake.

BRANCH=cr50, cr50-mp
BUG=none
TEST=size of the generated Cr50 image remains the same before and
     after this patch.

Change-Id: I31d5bffdc9b5109f1d4bb929dea66834a3bfa660
Signed-off-by: Vadim Bendebury <5515d6d2d0829cbe0dd0dcf2094aaded06d58514@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/1925681
Reviewed-by: Nicolas Boichat <f3daba1cdc403799935674d3cd4b0e5bd1804232@chromium.org>

coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec