[flang] Fix build warning from newer compilers

[klausler]

Summary

Remove a lambda capture of "[this]" in two cases where it
is no longer required. Will be pushed without waiting for
review if CI is successful in order to resolve a sad build bot.

flang/runtime/io-stmt.cpp

void IoStatementState::HandleRelativePosition(std::int64_t n) {
   common::visit([=](auto &x) { x.get().HandleRelativePosition(n); }, u_);
 }
 
 void IoStatementState::HandleAbsolutePosition(std::int64_t n) {
   common::visit([=](auto &x) { x.get().HandleAbsolutePosition(n); }, u_);
 }
 
 void IoStatementState::CompleteOperation() {
-  common::visit([this](auto &x) { x.get().CompleteOperation(); }, u_);
+  common::visit([](auto &x) { x.get().CompleteOperation(); }, u_);
 }
 
 int IoStatementState::EndIoStatement() {
-  return common::visit(
-      [this](auto &x) { return x.get().EndIoStatement(); }, u_);
+  return common::visit([](auto &x) { return x.get().EndIoStatement(); }, u_);
 }
 
 ConnectionState &IoStatementState::GetConnectionState() {
   return common::visit(
       [](auto &x) -> ConnectionState & { return x.get().GetConnectionState(); },
       u_);
 }