layout.conf: ban older EAPIs

BUG=None
TEST=CQ passes

Change-Id: I9540c3be4c7df93f5b99646956795ad960efa091
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/overlays/toolchains/+/4753663
Commit-Queue: Mike Frysinger <vapier@chromium.org>
Auto-Submit: Mike Frysinger <vapier@chromium.org>
Commit-Queue: Lee Presland <zland@google.com>
Tested-by: Mike Frysinger <vapier@chromium.org>
Reviewed-by: Lee Presland <zland@google.com>
diff --git a/metadata/layout.conf b/metadata/layout.conf
index 713acba..76b78cb 100644
--- a/metadata/layout.conf
+++ b/metadata/layout.conf
@@ -1,4 +1,5 @@
 cache-format = md5-dict
+eapis-banned = 0 1 2 3 4 5 6
 masters = portage-stable eclass-overlay chromiumos
 profile-formats = portage-2 profile-default-eapi profile-bashrcs
 profile_eapi_when_unspecified = 5-progress