[flang] Fix build warning from newer compilers

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.

Differential Revision: https://reviews.llvm.org/D131506

Author: klausler

flang/runtime/io-stmt.cpp

@@ -456,12 +456,11 @@ void IoStatementState::HandleAbsolutePosition(std::int64_t n) {
 }
 
 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() {