Don't preset SwAuthorityField::m_SortKeyArr with three empty elements

This appears to be a mistake introduced with
0be2a98c "Convert V_DECL_PTRARR_DEL(SortKeyArr)
to boost::ptr_vector", where the original svl/svarray.hxx-based SortKeyArr ctor
had a parameter specifying the initial capacity.

But the mistake was apparently harmless as uses of SwAuthorityField appear to
always fill m_SortKeyArr via SwAuthorityFieldType::PutValue or
SwAuthorityFieldType::SetSortKeys (which both first clear m_SortKeyArr) before
accessing m_SortKeyArr otherwise (as observed when playing around with Writer
"Insert - Table of Contents and Index - Table of Contents, Index or
Bibliography...", and in the "Table of Contents, Index or Bibliography" dialog
doing "Type - Type and Title - Type: Bibliography", "Entries - Sort by -
Content", "Entries - Sort Keys - 1: Address", etc.).

Change-Id: I0901b3b790f8390e743d5802116f13e7261e83eb
Reviewed-on: https://gerrit.libreoffice.org/48563Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>
Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>

sw/source/core/fields/authfld.cxx

@@ -66,7 +66,6 @@ bool    SwAuthEntry::operator==(const SwAuthEntry& rComp)
 SwAuthorityFieldType::SwAuthorityFieldType(SwDoc* pDoc)
     : SwFieldType( SwFieldIds::TableOfAuthorities ),
     m_pDoc(pDoc),
-    m_SortKeyArr(3),
     m_cPrefix('['),
     m_cSuffix(']'),
     m_bIsSequence(false),