checkout-release: Stop force-deleting branches

This was leftover from some bizarre hack I had in place. No need for this now.

Change-Id: Icb80226fcf91c22318df606d0ef818d682b69fcb
diff --git a/checkout-release.sh b/checkout-release.sh
index 718d798..0a252f6 100755
--- a/checkout-release.sh
+++ b/checkout-release.sh
@@ -19,7 +19,6 @@
     while read project commit; do
         pushd $project
         git checkout $commit
-        git branch -D --force $release_branch_name
         git checkout -b $release_branch_name
         popd
     done