D5369: rust: make clean takes care of rust/target

[Yuya Nishihara]

Queued, thanks.

Can you check ui.username is configured properly in your ~/hgrc?
Currently the patch author is set to "Georges Racinet on $hostname <$email>".

>  	rm -rf build mercurial/locale
>  	$(MAKE) -C doc clean
>  	$(MAKE) -C contrib/chg distclean
> +	if test -d rust/target; then rm -rf rust/target; fi

Removed "if ..". rm -rf shouldn't fail.