[DWARF] Remove unused declaration verifyIndexes

The declaration was added without a corresponding function definition
by:

  commit 0d8cb8b
  Author: David Blaikie <dblaikie@gmail.com>
  Date:   Thu May 5 18:09:34 2022 +0000

llvm/include/llvm/DebugInfo/DWARF/DWARFVerifier.h

@@ -156,7 +156,6 @@ class DWARFVerifier {
   unsigned verifyUnitSection(const DWARFSection &S);
   unsigned verifyUnits(const DWARFUnitVector &Units);
 
-  unsigned verifyIndexes(const DWARFObject &DObj);
   unsigned verifyIndex(StringRef Name, DWARFSectionKind SectionKind,
                        StringRef Index);