Revert "Limit outgoing to_device EDU size to 65536"

[erikjohnston]

Reverts #18416

Unfortunately, this causes failures on /sendToDevice endpoint in normal circumstances. If a single user has, say, a hundred devices then we easily go over the limit. This blocks message sending entirely in encrypted rooms.

cc @MadLittleMods @MatMaul

[MatMaul]

Humm sorry for that, annoying.

We could also split the map of devices for a single user.

[MatMaul]

I'll probably not be able to do so before the next RC however so let's revert indeed.

[erikjohnston]

Humm sorry for that, annoying.

It happens!

We could also split the map of devices for a single user.

I think there are a few things we can do:

1. Split the map of devices up
2. For EDUs that can't be split up, send in their own transaction (so long as its lower than the max request size)
3. Add a proper hard-error when a client tries and sends a to-device message that is too big to fit into a transaction. I very much doubt any existing to-device message being sent is anywhere near the limit