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>
diff --git a/sdk_lib/make_chroot.sh b/sdk_lib/make_chroot.sh
index e955d76..a2edead 100755
--- a/sdk_lib/make_chroot.sh
+++ b/sdk_lib/make_chroot.sh
@@ -39,8 +39,6 @@
 DEFINE_boolean delete $FLAGS_FALSE "Delete an existing chroot."
 DEFINE_boolean replace $FLAGS_FALSE "Overwrite existing chroot, if any."
 DEFINE_integer jobs -1 "How many packages to build in parallel at maximum."
-DEFINE_string stage3_date "2010.03.09" \
-  "Use the stage3 with the given date."
 DEFINE_string stage3_path "" \
   "Use the stage3 located on this path."
 DEFINE_string cache_dir "" "Directory to store caches within."