docker/conf/scheduler: Update scheduling policies

Remove overridden scheduling policies for opam origins as default ones
have been updated in swh-scheduler source code.

Override scheduling policies for git origins by using the default ones
without table sampling as listed_origins table in scheduler database
has usually a small size in docker environment and thus a low sampling
value does not return any origins when querying the table.

docker/conf/scheduler.yml

@@ -7,8 +7,13 @@ celery:
   broker_transport_options:
     max_retries: 1
 no_origins_scheduled_backoff: 60
-# ensure opam origin loading tasks will be scheduled
 scheduling_policy:
-  opam:
+  git:
+    # override git origin scheduling policies, same as default ones
+    # but without table sampling
+    - policy: already_visited_order_by_lag
+      weight: 49
+    - policy: never_visited_oldest_update_first
+      weight: 49
     - policy: origins_without_last_update
-      weight: 100
+      weight: 2