According to:

<mst_> noelgrandin: apparently this code exists so you can export a text

     frame as an image and then the urls in the text become
    image-map links

which means that according to my analysis below, nobody has noticed the
removal in 17 years :-)

SwNoteURL::InsertURLNote was the last place that constructed an
SwNoteURL and it was removed in
    commit bb7ade14
    Author: Noel Grandin <noel.grandin@collabora.co.uk>
    Date:   Wed Mar 7 13:42:58 2018 +0200
    loplugin:unusedmethods

and SwNoteURL::InsertURLNote was dead because
   void SwTextPaintInfo::NotifyURL_( const SwLinePortion &rPor ) const
was removed in
    commit 73139fe6
    Author: Noel Grandin <noel.grandin@collabora.co.uk>
    Date:   Fri Jan 19 13:10:22 2018 +0200
    loplugin:unusedmethods

and SwTextPaintInfo::NotifyURL_ was dead because
   void SwTextPaintInfo::NotifyURL( const SwLinePortion &rPor ) const
was removed in
    commit be8c4145
    Author: Noel Grandin <noel.grandin@collabora.co.uk>
    Date:   Fri Jan 19 09:13:03 2018 +0200
    loplugin:unusedmethods also check for functions returning bool

and NotifyURL was dead because calls to it were removed in
    commit 1b666235
    Author: Noel Grandin <noel.grandin@collabora.co.uk>
    Date:   Wed Jan 3 09:08:52 2018 +0200
    loplugin:singlevalfields improve copy constructor check
those calls were removed because the m_bURL field of SwFont was always
false.

tracing back, we find that m_bURL was called bURL before
    commit b4e2a13f
    Author: Miklos Vajna <vmiklos@collabora.co.uk>
    Date:   Mon Oct 26 08:55:17 2015 +0100
    sw: prefix members of SwFont

and we find that a method
     void SwFont::SetURL(const bool)
that modified bURL was removed in
    commit 407731c9
    Author: Noel Grandin <noel@peralex.com>
    Date:   Tue Jul 21 10:44:17 2015 +0200
    loplugin:unusedmethods sw

and we find that calls to SetURL were removed in
    commit da7671e4
    Author: Andreas Martens <ama@openoffice.org>
    Date:   Thu Mar 15 14:59:12 2001 +0000
    Opt.(FME): The new attribute handler makes a lot of code superfluous

which appears to be the root of the problem

Change-Id: Id2362ce216c06bc8dcf71698695d708eb494af4e
Reviewed-on: https://gerrit.libreoffice.org/51225Reviewed-by: Michael Stahl <mstahl@redhat.com>
Tested-by: Jenkins <ci@libreoffice.org>