CA-404020: Do not fail when removing a non-existing datasource

The latest changes in the metrics daemon changes how archived and live metrics
are synchronised, and archived sources are created less often. This meant that
on some cases, like SR.forget, the operations failed because they could query
for existing sources, but the call to remove them failed, because the metrics
only exist in live form, not archived one.

(what happens with the live one, do they disappear when the SR is forgotten?)

Signed-off-by: Pau Ruiz Safont <[email protected]>

ocaml/libs/xapi-rrd/lib/rrd.ml

@@ -632,13 +632,14 @@ let rrd_add_ds rrd timestamp newds =
   else
     rrd_add_ds_unsafe rrd timestamp newds
 
-(** Remove the named DS from an RRD. Removes all of the data associated with it, too *)
+(** Remove the named DS from an RRD. Removes all of the data associated with
+    it, too. THe function is idempotent. *)
 let rrd_remove_ds rrd ds_name =
   let n =
     Utils.array_index ds_name (Array.map (fun ds -> ds.ds_name) rrd.rrd_dss)
   in
   if n = -1 then
-    raise (Invalid_data_source ds_name)
+    rrd
   else
     {
       rrd with