Remove BisonWrap, which was a Ptr-specific feature (#836)

executable_semantics/syntax/bison_wrap.h

@@ -1,44 +0,0 @@
-// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
-// Exceptions. See /LICENSE for license information.
-// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
-
-#ifndef EXECUTABLE_SEMANTICS_SYNTAX_BISON_WRAP_H_
-#define EXECUTABLE_SEMANTICS_SYNTAX_BISON_WRAP_H_
-
-#include <optional>
-
-#include "common/check.h"
-
-namespace Carbon {
-
-// Bison requires that types be default initializable for use with its variant
-// semantics. This wraps arbitrary types to support a default constructor, while
-// still requiring they be properly initialized.
-template <typename T>
-class BisonWrap {
- public:
-  // Assigning a value initializes the wrapper.
-  BisonWrap& operator=(T&& rhs) {
-    val = std::move(rhs);
-    return *this;
-  }
-
-  // Support transparent conversion to the wrapped type.
-  operator T() { return Release(); }
-
-  // Deliberately releases the contained value. Errors if not initialized.
-  // Called directly in parser.ypp when releasing pairs.
-  auto Release() -> T {
-    CHECK(val.has_value());
-    T ret = std::move(*val);
-    val.reset();
-    return ret;
-  }
-
- private:
-  std::optional<T> val;
-};
-
-}  // namespace Carbon
-
-#endif  // EXECUTABLE_SEMANTICS_SYNTAX_BISON_WRAP_H_