Remove the chromium.goma.migration console.

The chromium.goma.migration console was used for tracking the migration
of chromium builders to the RBE backend. The migration was completed
some time ago and so the manually curated console is an unnecessary
touch point when removing or renaming builders.

Change-Id: I41c1b9a3e418b371a71e2830accb6919f684e063
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2411328
Auto-Submit: Garrett Beaty <gbeaty@chromium.org>
Reviewed-by: Yoshisato Yanagisawa <yyanagisawa@chromium.org>
Commit-Queue: Yoshisato Yanagisawa <yyanagisawa@chromium.org>
Cr-Commit-Position: refs/heads/master@{#806797}

infra/config/subprojects/goma/subproject.star

@@ -5,6 +5,5 @@
 exec("./goma.star")
 exec("./consoles/chromium.goma.star")
 exec("./consoles/chromium.goma.fyi.star")
-exec("./consoles/chromium.goma.migration.star")
 exec("./consoles/goma.latest.star")
 exec("./consoles/luci.chromium.goma.star")