Remove a misplaced comment

This comment provides general information about how MessagePorts work,
but isn't directly related to any of the surrounding code.

Of the two comments here, the second one is the most useful information
to consumers of the PortProvider and PortFinder interfaces, but it is
well covered by eg. MDN's documentation on MessagePort.

src/shared/port-provider.js

@@ -76,12 +76,6 @@ export class PortProvider {
     /** @type {Map<Channel, WeakMap<Window, MessageChannel>>} */
     this._channels = new Map();
 
-    // Two important characteristics of `MessagePort`:
-    // - Once created, a MessagePort can only be transferred to a different
-    //   frame once, and if any frame attempts to transfer it again it gets
-    //   neutered.
-    // - Messages are queued until the other port is ready to listen (`port.start()`)
-
     // Create the `sidebar-host` channel immediately, while other channels are
     // created on demand
     this._sidebarHostChannel = new MessageChannel();