Remove the milestone entry for M109.

M109 was being kept around for supporting versions of Windows before
Windows 10 since support for those versions was removed in M110. That
extended period of support has ended, so it is no longer necessary.

Bug: 1406951
Change-Id: I61a91f7d3dbd69fa4109022ea492590d16ba9860
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4969892
Commit-Queue: Garrett Beaty <gbeaty@google.com>
Reviewed-by: Ben Pastene <bpastene@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1213786}

infra/config/generated/luci/commit-queue.cfg

@@ -5337,7 +5337,6 @@ config_groups {
     projects {
       name: "chromium/src"
       ref_regexp: "refs/branch-heads/.*"
-      ref_regexp_exclude: "refs/branch-heads/5414"
       ref_regexp_exclude: "refs/branch-heads/5735"
       ref_regexp_exclude: "refs/branch-heads/5845"
       ref_regexp_exclude: "refs/branch-heads/5938"