Remove duplicate header comment that resulted from build time module-boundary wrapper code

[bvaughn]

Resolves #22673

Also fixes the scope of 'use strict'; (which had been moved below the header in the previous commit, which I think breaks its functionality).

---

Before I added the module boundary wrappers:

/** @license React vundefined
 * react.development.js
 *
 * Copyright (c) Facebook, Inc. and its affiliates.
 *
 * This source code is licensed under the MIT license found in the
 * LICENSE file in the root directory of this source tree.
 */

'use strict';

if (process.env.NODE_ENV !== "production") {
  (function() {
'use strict';

var _assign = require('object-assign');

// Other code ...

exports.version = ReactVersion;
  })();
}

---

Before the changes in this PR (with module wrappers):

/** @license React vundefined
 * react.development.js
 *
 * Copyright (c) Facebook, Inc. and its affiliates.
 *
 * This source code is licensed under the MIT license found in the
 * LICENSE file in the root directory of this source tree.
 */

'use strict';

if (process.env.NODE_ENV !== "production") {
  (function() {

          /**
 * Copyright (c) Facebook, Inc. and its affiliates.
 *
 * This source code is licensed under the MIT license found in the
 * LICENSE file in the root directory of this source tree.
 */

/* global __REACT_DEVTOOLS_GLOBAL_HOOK__ */

// Don't require this file directly; it's embedded by Rollup during build.

if (
  typeof __REACT_DEVTOOLS_GLOBAL_HOOK__ !== 'undefined' &&
  typeof __REACT_DEVTOOLS_GLOBAL_HOOK__.registerInternalModuleStart ===
    'function'
) {
  __REACT_DEVTOOLS_GLOBAL_HOOK__.registerInternalModuleStart(new Error());
}
          'use strict';

var _assign = require('object-assign');

// ...

exports.version = ReactVersion;
          /**
 * Copyright (c) Facebook, Inc. and its affiliates.
 *
 * This source code is licensed under the MIT license found in the
 * LICENSE file in the root directory of this source tree.
 */

/* global __REACT_DEVTOOLS_GLOBAL_HOOK__ */

// Don't require this file directly; it's embedded by Rollup during build.

if (
  typeof __REACT_DEVTOOLS_GLOBAL_HOOK__ !== 'undefined' &&
  typeof __REACT_DEVTOOLS_GLOBAL_HOOK__.registerInternalModuleStop ===
    'function'
) {
  __REACT_DEVTOOLS_GLOBAL_HOOK__.registerInternalModuleStop(new Error());
}
        
  })();
}

---

After the changes in this PR:

/** @license React vundefined
 * react.development.js
 *
 * Copyright (c) Facebook, Inc. and its affiliates.
 *
 * This source code is licensed under the MIT license found in the
 * LICENSE file in the root directory of this source tree.
 */

'use strict';

if (process.env.NODE_ENV !== "production") {
  (function() {

          'use strict';

/* global __REACT_DEVTOOLS_GLOBAL_HOOK__ */
if (
  typeof __REACT_DEVTOOLS_GLOBAL_HOOK__ !== 'undefined' &&
  typeof __REACT_DEVTOOLS_GLOBAL_HOOK__.registerInternalModuleStart ===
    'function'
) {
  __REACT_DEVTOOLS_GLOBAL_HOOK__.registerInternalModuleStart(new Error());
}
          var _assign = require('object-assign');

// ...

// Other code ...

exports.version = ReactVersion;
          /* global __REACT_DEVTOOLS_GLOBAL_HOOK__ */
if (
  typeof __REACT_DEVTOOLS_GLOBAL_HOOK__ !== 'undefined' &&
  typeof __REACT_DEVTOOLS_GLOBAL_HOOK__.registerInternalModuleStop ===
    'function'
) {
  __REACT_DEVTOOLS_GLOBAL_HOOK__.registerInternalModuleStop(new Error());
}
        
  })();
}