Clean up xapi_xenops and more (#6543)

Best reviewed by commit, and also best viewed locally with a git client
that distinguishes between moved and new lines, with a config like:
```
[diff]
    colormoved = "default"
    colormovedws = "allow-indentation-change"
```

No functional changes intended.

----

This is split out from a larger series, but I figured these cleanups are
easier to review on their own and it would be better to get them in
early to avoid annoying rebases of a thousand lines of code ....

Author: last-genius

ocaml/xapi-idl/xen/xenops_interface.ml

@@ -444,16 +444,6 @@ module Dynamic = struct
 
   type barrier = int * id list [@@deriving rpcty]
 
-  type t =
-    | Vm_t of Vm.id * (Vm.t * Vm.state) option
-    | Vbd_t of Vbd.id * (Vbd.t * Vbd.state) option
-    | Vif_t of Vif.id * (Vif.t * Vif.state) option
-    | Pci_t of Pci.id * (Pci.t * Pci.state) option
-    | Vgpu_t of Vgpu.id * (Vgpu.t * Vgpu.state) option
-    | Vusb_t of Vusb.id * (Vusb.t * Vusb.state) option
-    | Task_t of Task.id * Task.t option
-  [@@deriving rpcty]
-
   let rpc_of_id = Rpcmarshal.marshal id.Rpc.Types.ty
 end