[server] use Db.yield API

src/plugins/server/main.ml

@@ -333,7 +333,7 @@ let run server =
           if not activity then
             begin
               Unix.sleepf idle_s ;
-              !Db.progress () ;
+              Db.yield () ;
             end
         done ;
       with Sys.Break -> () (* Ctr+C, just leave the loop normally *)

src/plugins/server/server_parameters.ml

@@ -45,14 +45,6 @@ module Idle = P.Int
       let help = "Server polling (in milliseconds, default 50ms)"
     end)
 
-module Yield = P.Int
-    (struct
-      let option_name = "-server-yield"
-      let arg_name = "ms"
-      let default = 50
-      let help = EXEC yield period (in milliseconds, default 50ms)"
-    end)
-
 module AutoLog = P.False
     (struct
       let option_name = "-server-auto-log"