[flang][OpenMP] Remove `OmpEndLoopDirective` handles from code.

[SouraVX]

Summary

This directive is currently lowered as NOP.

Patch is an attempt upstream code from:
PR: https://github.com/flang-compiler/f18-llvm-project/pull/573

[kiranchandramohan]

LGTM.

Removes some code which is not used and will not be used.

flang/include/flang/Lower/OpenMP.h

 //===----------------------------------------------------------------------===//
 
 #ifndef FORTRAN_LOWER_OPENMP_H
 #define FORTRAN_LOWER_OPENMP_H
 
 namespace Fortran {
 namespace parser {
 struct OpenMPConstruct;
-struct OmpEndLoopDirective;
 } // namespace parser
 
 namespace lower {
 
 class AbstractConverter;
 
 namespace pft {
 struct Evaluation;
 } // namespace pft
 
 void genOpenMPConstruct(AbstractConverter &, pft::Evaluation &,
                         const parser::OpenMPConstruct &);
 
-void genOpenMPEndLoop(AbstractConverter &, pft::Evaluation &,
-                      const parser::OmpEndLoopDirective &);
-
 } // namespace lower
 } // namespace Fortran
 
 #endif // FORTRAN_LOWER_OPENMP_H

flang/lib/Lower/OpenMP.cpp

std::visit(
           },
           [&](const Fortran::parser::OpenMPCriticalConstruct
                   &criticalConstruct) {
             TODO(converter.getCurrentLocation(), "OpenMPCriticalConstruct");
           },
       },
       ompConstruct.u);
 }
-
-void Fortran::lower::genOpenMPEndLoop(
-    Fortran::lower::AbstractConverter &converter,
-    Fortran::lower::pft::Evaluation &,
-    const Fortran::parser::OmpEndLoopDirective &) {
-  TODO(converter.getCurrentLocation(), "OmpEndLoopDirective");
-}