[flang][OpenMP] Remove unused class OmpMemoryOrderClause, NFC (#151759)

flang/examples/FeatureList/FeatureList.cpp

diff --git a/flang/examples/FeatureList/FeatureList.cpp b/flang/examples/FeatureList/FeatureList.cpp
index 0b8066e..b686430 100644
--- a/flang/examples/FeatureList/FeatureList.cpp
+++ b/flang/examples/FeatureList/FeatureList.cpp
@@ -554,7 +554,6 @@
   READ_FEATURE(OpenMPDeclareSimdConstruct)
   READ_FEATURE(OpenMPDeclareTargetConstruct)
   READ_FEATURE(OmpMemoryOrderType)
-  READ_FEATURE(OmpMemoryOrderClause)
   READ_FEATURE(OmpAtomicDefaultMemOrderClause)
   READ_FEATURE(OpenMPFlushConstruct)
   READ_FEATURE(OpenMPLoopConstruct)

flang/include/flang/Parser/dump-parse-tree.h

diff --git a/flang/include/flang/Parser/dump-parse-tree.h b/flang/include/flang/Parser/dump-parse-tree.h
index 68e402c..2c666a6 100644
--- a/flang/include/flang/Parser/dump-parse-tree.h
+++ b/flang/include/flang/Parser/dump-parse-tree.h
@@ -721,7 +721,6 @@
   NODE(parser, OpenMPDeclareTargetConstruct)
   NODE(parser, OpenMPDeclareMapperConstruct)
   NODE_ENUM(common, OmpMemoryOrderType)
-  NODE(parser, OmpMemoryOrderClause)
   NODE(parser, OmpAtomicDefaultMemOrderClause)
   NODE(parser, OpenMPDepobjConstruct)
   NODE(parser, OpenMPUtilityConstruct)

flang/include/flang/Parser/parse-tree.h

diff --git a/flang/include/flang/Parser/parse-tree.h b/flang/include/flang/Parser/parse-tree.h
index 7807db4..8302e40 100644
--- a/flang/include/flang/Parser/parse-tree.h
+++ b/flang/include/flang/Parser/parse-tree.h
@@ -270,7 +270,6 @@
 struct OpenMPLoopConstruct;
 struct OpenMPDeclarativeConstruct;
 struct OmpEndLoopDirective;
-struct OmpMemoryOrderClause;
 struct CUFKernelDoConstruct;
 
 // Cooked character stream locations
@@ -5016,17 +5015,6 @@
       OpenMPAllocatorsConstruct, OmpBlockConstruct);
 };
 
-// 2.17.7 Atomic construct/2.17.8 Flush construct [OpenMP 5.0]
-//        memory-order-clause -> acq_rel
-//                               acquire
-//                               release
-//                               relaxed
-//                               seq_cst
-struct OmpMemoryOrderClause {
-  WRAPPER_CLASS_BOILERPLATE(OmpMemoryOrderClause, OmpClause);
-  CharBlock source;
-};
-
 struct OpenMPAtomicConstruct : public OmpBlockConstruct {
   llvm::omp::Clause GetKind() const;
   bool IsCapture() const;

flang/lib/Parser/openmp-parsers.cpp

diff --git a/flang/lib/Parser/openmp-parsers.cpp b/flang/lib/Parser/openmp-parsers.cpp
index 7daba33..84d1e81 100644
--- a/flang/lib/Parser/openmp-parsers.cpp
+++ b/flang/lib/Parser/openmp-parsers.cpp
@@ -1619,20 +1619,6 @@
 TYPE_PARSER(sourced( //
     construct<OpenMPAtomicConstruct>(OmpAtomicConstructParser{})))
 
-// 2.17.7 Atomic construct/2.17.8 Flush construct [OpenMP 5.0]
-//        memory-order-clause ->
-//                               acq_rel
-//                               acquire
-//                               relaxed
-//                               release
-//                               seq_cst
-TYPE_PARSER(sourced(construct<OmpMemoryOrderClause>(
-    sourced("ACQ_REL" >> construct<OmpClause>(construct<OmpClause::AcqRel>()) ||
-        "ACQUIRE" >> construct<OmpClause>(construct<OmpClause::Acquire>()) ||
-        "RELAXED" >> construct<OmpClause>(construct<OmpClause::Relaxed>()) ||
-        "RELEASE" >> construct<OmpClause>(construct<OmpClause::Release>()) ||
-        "SEQ_CST" >> construct<OmpClause>(construct<OmpClause::SeqCst>())))))
-
 static bool IsSimpleStandalone(const OmpDirectiveName &name) {
   switch (name.v) {
   case llvm::omp::Directive::OMPD_barrier:

flang/lib/Parser/unparse.cpp

diff --git a/flang/lib/Parser/unparse.cpp b/flang/lib/Parser/unparse.cpp
index 44f31ca..46141e2 100644
--- a/flang/lib/Parser/unparse.cpp
+++ b/flang/lib/Parser/unparse.cpp
@@ -2801,7 +2801,6 @@
     EndOpenMP();
   }
   void Unparse(const OmpFailClause &x) { Walk(x.v); }
-  void Unparse(const OmpMemoryOrderClause &x) { Walk(x.v); }
   void Unparse(const OmpMetadirectiveDirective &x) {
     BeginOpenMP();
     Word("!$OMP METADIRECTIVE ");