Remove the lock-file-link-count test from the XML backend.

This was an effort of somewhat dubious value to detect if a process
on another ocmputer had a hsrd-link to a lockfile on an NFS share.
NFS is rarely used now and SMB doesn't support hard links so this check
adds complexity with no real value.

libgnucash/backend/xml/gnc-xml-backend.cpp

@@ -669,90 +669,7 @@ GncXmlBackend::get_file_lock ()
         return false;
     }
 
-    /* OK, now work around some NFS atomic lock race condition
-     * mumbo-jumbo.  We do this by linking a unique file, and
-     * then examining the link count.  At least that's what the
-     * NFS programmers guide suggests.
-     * Note: the "unique filename" must be unique for the
-     * triplet filename-host-process, otherwise accidental
-     * aliases can occur.
-     */
-
-    /* apparently, even this code may not work for some NFS
-     * implementations. In the long run, I am told that
-     * ftp.debian.org
-     *  /pub/debian/dists/unstable/main/source/libs/liblockfile_0.1-6.tar.gz
-     * provides a better long-term solution.
-     */
-
-#ifndef G_OS_WIN32
-    auto path = m_lockfile.find_last_of('.');
-    std::stringstream linkfile;
-    if (path != std::string::npos)
-        linkfile << m_lockfile.substr(0, path);
-    else
-        linkfile << m_lockfile;
-    linkfile << "." << gethostid() << "." << getpid() << ".LNK";
-    rc = link (m_lockfile.c_str(), linkfile.str().c_str());
-    if (rc)
-    {
-        /* If hard links aren't supported, just allow the lock. */
-        if (errno == EPERM || errno == ENOSYS
-# ifdef EOPNOTSUPP
-            || errno == EOPNOTSUPP
-# endif
-# ifdef ENOTSUP
-            || errno == ENOTSUP
-# endif
-           )
-        {
-            return true;
-        }
-
-        /* Otherwise, something else is wrong. */
-        set_error(ERR_BACKEND_LOCKED);
-        g_unlink (linkfile.str().c_str());
-        close (m_lockfd);
-        m_lockfd = -1;
-        g_unlink (m_lockfile.c_str());
-        m_lockfile.clear();
-        return false;
-    }
-
-    rc = g_stat (m_lockfile.c_str(), &statbuf);
-    if (rc)
-    {
-        /* oops .. stat failed!  This can't happen! */
-        set_error(ERR_BACKEND_LOCKED);
-        std::string msg{"Failed to stat lockfile "};
-        set_message(msg + m_lockfile);
-        g_unlink (linkfile.str().c_str());
-        close (m_lockfd);
-        m_lockfd = -1;
-        g_unlink (m_lockfile.c_str());
-        m_lockfile.clear();
-        return false;
-    }
-
-    if (statbuf.st_nlink != 2)
-    {
-        set_error(ERR_BACKEND_LOCKED);
-        g_unlink (linkfile.str().c_str());
-        close (m_lockfd);
-        m_lockfd = -1;
-        g_unlink (m_lockfile.c_str());
-        m_lockfile.clear();
-        return false;
-    }
-
-    m_linkfile = linkfile.str();
-    return true;
-
-#else /* ifndef G_OS_WIN32 */
-    /* On windows, there is no NFS and the open(,O_CREAT | O_EXCL)
-       is sufficient for locking. */
     return true;
-#endif /* ifndef G_OS_WIN32 */
 }
 
 bool