Revert "message_edit: Use `disabled` instead of `readonly` to disable controls."
Revert "message_edit: Use `disabled` instead of `readonly` to disable controls."

This appears to have broken "Copy and close" in "View source".

This reverts commit 73cfab8ba8b56a146e4028579b53c28cc8c6e4e0.

rht/zulip,rht/zulip,andersk/zulip,zulip/zulip,zulip/zulip,rht/zulip,rht/zulip,zulip/zulip,rht/zulip,andersk/zulip,rht/zulip,rht/zulip,andersk/zulip,zulip/zulip,andersk/zulip,zulip/zulip,andersk/zulip,andersk/zulip,andersk/zulip,zulip/zulip,zulip/zulip