Bug 4433: Small display problem for topical subjects

Bug 4433: Small display problem for topical subjects

This removes the subfield codes shown for topical subject authorities only.

To test:
- Add different authority records and at least one for a topical subject.
- Use search in intranet and opac (turn on opacauthorities) to serch for your subjects.
- All headings will show without the subfield codes (at least $a in front), except the
topical subject.

This patch removes the subfield codes for the topical headings.

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Works as advertised in opac and staff. (July 18, 2011)

Signed-off-by: Chris Cormack <chrisc@catalyst.net.nz>