Moves stringToArrayBuffer into util folder

js/modules/string_to_array_buffer.d.ts

@@ -1,4 +0,0 @@
-// Copyright 2020 Signal Messenger, LLC
-// SPDX-License-Identifier: AGPL-3.0-only
-
-export function stringToArrayBuffer(string: string): ArrayBuffer;

js/modules/string_to_array_buffer.js

@@ -1,14 +0,0 @@
-// Copyright 2018-2020 Signal Messenger, LLC
-// SPDX-License-Identifier: AGPL-3.0-only
-
-exports.stringToArrayBuffer = string => {
-  if (typeof string !== 'string') {
-    throw new TypeError("'string' must be a string");
-  }
-
-  const array = new Uint8Array(string.length);
-  for (let i = 0; i < string.length; i += 1) {
-    array[i] = string.charCodeAt(i);
-  }
-  return array.buffer;
-};