Revert "Use protocol buffer module for libtextsecure"

This does not work with `ArrayBuffer` out of the box and will need to be
investigated and tested more before switching.

Some APIs also seemed to have changed:
- Before (OOP): `new textsecure.protobuf.WebSocketMessage(…).encode();`
- After (functional):
  ```
  textsecure.protobuf.WebSocketMessage.encode(
    new textsecure.protobuf.WebSocketMessage(…)
  );
  ```

This reverts commit d758119d9de4f99742ea941e86180b1d600c2f22.

libtextsecure/protobufs.js

@@ -0,0 +1,42 @@
+(function() {
+  'use strict';
+  window.textsecure = window.textsecure || {};
+  window.textsecure.protobuf = {};
+
+  function loadProtoBufs(filename) {
+    return dcodeIO.ProtoBuf.loadProtoFile(
+      { root: window.PROTO_ROOT, file: filename },
+      function(error, result) {
+        if (error) {
+          var text =
+            'Error loading protos from ' +
+            filename +
+            ' (root: ' +
+            window.PROTO_ROOT +
+            ') ' +
+            (error && error.stack ? error.stack : error);
+          console.log(text);
+          throw error;
+        }
+        var protos = result.build('signalservice');
+        if (!protos) {
+          var text =
+            'Error loading protos from ' +
+            filename +
+            ' (root: ' +
+            window.PROTO_ROOT +
+            ')';
+          console.log(text);
+          throw new Error(text);
+        }
+        for (var protoName in protos) {
+          textsecure.protobuf[protoName] = protos[protoName];
+        }
+      }
+    );
+  }
+
+  loadProtoBufs('SignalService.proto');
+  loadProtoBufs('SubProtocol.proto');
+  loadProtoBufs('DeviceMessages.proto');
+})();

libtextsecure/test/index.html

@@ -18,6 +18,7 @@
   <script type="text/javascript" src="../components.js"></script>
   <script type="text/javascript" src="../libsignal-protocol.js"></script>
   <script type="text/javascript" src="../crypto.js"></script>
+  <script type="text/javascript" src="../protobufs.js" data-cover></script>
   <script type="text/javascript" src="../errors.js" data-cover></script>
   <script type="text/javascript" src="../storage.js" data-cover></script>
   <script type="text/javascript" src="../protocol_wrapper.js" data-cover></script>