I was getting a compiler warning from it:

CTranslatorUtils.cpp: In static member function ‘static gpos::BOOL gpdxl::CTranslatorUtils::IsGroupingColumn(const SortGroupClause*, List*)’:
CTranslatorUtils.cpp:2079:42: warning: self-comparison always evaluates to true [-Wtautological-compare]
   if (sort_group_clause->tleSortGroupRef == sort_group_clause->tleSortGroupRef)
       ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

But since the function doesn't seem to be used anywhere, let's just remove
it, instead of trying to fix it.