contrib/noupdate does not work and never has worked

Forwarded from a response on pgsql-sql:

> I thought that the idea behind noup was to protect single columns from
> update. However, when I apply the noup trigger as above, I can't
> update /any/ column. Is this the intended behaviour?

Idly looking at the source code for contrib/noupdate/noup.c, I don't
believe that it has ever worked as advertised: it seems to reject any
non-null value for the target column, independently of whether the
value is the same as before (which is what I'd have thought it should
do).

Is anyone interested in fixing it? Or should we just remove it?
If it's been there since 6.4 and you're the first person to try to use
it, as seems to be the case, then I'd have to say that it's a waste of
space in the distribution.

regards, tom lane