Revert "Leave out optional keys from /sync (#9919)"

[erikjohnston]

This reverts commit e9eb354 / #9919

The PR breaks Element iOS push, as its handling expects some of the keys to be there. We revert while they fix it and put out a new release.

[manuroe]

iOS issue: element-hq/element-ios#4309

[deepbluev7]

Do I need to do anything to get that back in in a few weeks then or will that be done automatically? :3

[callahad]

Do I need to do anything to get that back in in a few weeks then or will that be done automatically? :3

I've filed #9941 to track re-introducing that change. The Z-Future-Maintenance label ensures we'll look at it every two weeks during release planning, and, when things are ready, we'll pull it back in :)

[deepbluev7]

Thank you!