Bug 8823: CatalogModuleRelink Creates Multiple Links between Bib and Auth record

Bug 8823: CatalogModuleRelink Creates Multiple Links between Bib and Auth record

On 3.8.x, it was possible for multiple automatically generated
authorities to be linked to a single heading. This patch deletes
previous links from headings prior to linking them to
automatically-generated headings. This patch also corrects a
potential problem wherein multiple authorities might be generated if
a record is edited repeatedly in quick succession. The latter problem
exists on Master and 3.6.x as well, and the code that corrects the
multiple linkages is equally applicable if seemingly unnecessary.

Signed-off-by: Chris Cormack <chrisc@catalyst.net.nz>
Signed-off-by: Paul Poulain <paul.poulain@biblibre.com>