cleaning up some minor things

[Ricardo Wurmus]

Hi,

“guix/scripts/pull.scm” imports WITH-FILE-LOCK/NO-WAIT from (guix build
syscalls) but doesn’t use it.  Can we remove that?

“guix/store/deduplication.scm” defines a variant of DUMP-PORT with this
comment:

   ;; TODO: Remove once 'dump-port' in (guix build utils) has an optional 'len'
   ;; parameter.

The variant in (guix build utils) already supports that optional
argument.  Can we remove the variant in (guix store deduplication)?

-- 
Ricardo