Insufficiently documented deprecated command arguments

[Markus Armbruster]

I went through the QAPI schema looking for deprecated stuff not
mentioned in qemu-deprecated.texi.  Here's what I found:

    Commit b33945cfff "block: Accept device model name for
    blockdev-open/close-tray" (v2.8.0) deprecated blockdev-open-tray,
    blockdev-close-tray argument @device.

    Commit 70e2cb3bd7 "block: Accept device model name for
    blockdev-change-medium" (v2.8.0) deprecated blockdev-change-medium
    argument @device.

    Commit 7a9877a026 "block: Accept device model name for
    block_set_io_throttle" (v2.8.0) deprecated block_set_io_throttle
    argument @device.

    Commit c01c214b69 "block: remove all encryption handling APIs"
    (v2.10.0) deprecated query-named-block-nodes result field
    encryption_key_missing and query-block result field
    inserted.encryption_key_missing.

    Commit c42e8742f5 "block: Use JSON null instead of "" to disable
    backing file" (v2.10.0) deprecated blockdev-add empty string
    argument @backing.

    These were missed in commit eb22aeca65 "docs: document deprecation
    policy & deprecated features in appendix" (v2.10.0).

    Commit 3c605f4074 "commit: Add top-node/base-node options" (v3.1.0)
    deprecated block-commit arguments @base and @top.

I can update qemu-deprecated.texi for these.

Now my question: I wonder whether we want to remove any of them right
away.