[flang][runtime] Remove redundant initialization (#150984)

The assignment to mutableModes() in BeginIoStatement() is redundant,
since the mutableModes_ data member is initialized by the constructors
of the two classes that now have one. Remove the assignment to avoid
confusion.

Also restores the original OutputStatementState base class name after a
recent patch that needlessly changed it to something equivalent but less
readable.

Author: klausler

flang-rt/include/flang-rt/runtime/io-stmt.h

@@ -856,7 +856,7 @@ class InquireUnconnectedFileState : public NoUnitIoStatementState {
 };
 
 class InquireIOLengthState : public NoUnitIoStatementState,
-                             public IoDirectionState<Direction::Output> {
+                             public OutputStatementState {
 public:
   RT_API_ATTRS InquireIOLengthState(
       const char *sourceFile = nullptr, int sourceLine = 0);

flang-rt/lib/runtime/unit.h

@@ -161,9 +161,6 @@ class ExternalFileUnit : public ConnectionState,
     lock_.Take();
 #endif
     A &state{u_.emplace<A>(std::forward<X>(xs)...)};
-    if constexpr (!std::is_same_v<A, OpenStatementState>) {
-      state.mutableModes() = ConnectionState::modes;
-    }
     directAccessRecWasSet_ = false;
     io_.emplace(state);
     return *io_;