Do not clone IPXE since it's a submodule

buildbot/buildbot_steps.sh

@@ -480,12 +480,3 @@ function upload_release_ipxe_shasums() {
 
     return 0
 }
-
-if [[ ! "$(ps -o cmd -p $$ | tail -n 1 | tr -d '\n')" =~ "bash" ]]; then
-    >&2 echo "Shell not bash, exiting."
-    exit 1
-fi
-
-# This is a bash-specific hack to determine if the file is being sourced or
-# run as a script. It will only work in bash, not other shells.
-(return 0 2>/dev/null) || "$@"