make_chroot: drop unused stage3_date flag

This hasn't been used in years when the code in CL:193253 deleted it
all.  Clean up the command line flag too.

BUG=chromium:360346
TEST=precq passes

Change-Id: Icb555751f5af59a8dadd21d8a4d02c83936a8753
Reviewed-on: https://chromium-review.googlesource.com/1387713
Commit-Ready: Mike Frysinger <vapier@chromium.org>
Tested-by: Mike Frysinger <vapier@chromium.org>
Reviewed-by: Alex Klein <saklein@chromium.org>
1 file changed