fix: remove index.sort.field for internal metrics

illegal_argument_exception: [illegal_argument_exception] Reason: [index.mode=time_series]
is incompatible with [index.sort.field]

apmpackage/apm/data_stream/internal_metrics/manifest.yml

@@ -3,6 +3,7 @@ type: metrics
 dataset: apm.internal
 ilm_policy: metrics-apm.internal_metrics-default_policy
 elasticsearch:
+  index_mode: "time_series"
   index_template:
     mappings:
       # Internal metrics should have all fields strictly mapped;
@@ -21,8 +22,3 @@ elasticsearch:
                   type: aggregate_metric_double
                   metrics: [sum, value_count]
                   default_metric: sum
-    settings:
-      index:
-        mode: "time_series"
-        sort.field: "@timestamp"
-        sort.order: desc