get_gbb_flags.sh: Add removal notice message

futility can modify gbb flags directly now. Add a notice that the
scripts will be removed.

BUG=b:260531154
BRANCH=None
TEST=./get_gbb_flags.sh

Change-Id: I46a9a903c6f2e68f76b71fba4246e85feef9f2e9
Signed-off-by: Evan Benn <[email protected]>
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/vboot_reference/+/4170143
Reviewed-by: Yu-Ping Wu <[email protected]>
Reviewed-by: Edward O'Callaghan <[email protected]>
2 files changed