Delete `update-all-references` script

[oli-obk]

#50806 added the ./x.py test --bless flag which is better than the script in all ways except in having been used for a long time. Thus I left the scripts in the tree so we can use them if --bless fails.

Once this issue is a month old or so, we should delete the various copies of the update-reference and update-all-references scripts. (Unless --bless doesn't live up to its promise, then we should of course delay deleting the scripts).

[oli-obk]

Thanks @ccesare for cleaning this up