schema/stats: flow_mgr is actually flow.mgr

The schema accounts for a stats counters group that is a subgroup of the
flows stats counters. Remove `flow_mgr`, thus.

(cherry picked from commit 173fec81f8)

etc/schema.json

@@ -7547,51 +7547,6 @@
                         }
                     }
                 },
-                "flow_mgr": {
-                    "type": "object",
-                    "additionalProperties": false,
-                    "properties": {
-                        "bypassed_pruned": {
-                            "type": "integer"
-                        },
-                        "closed_pruned": {
-                            "type": "integer"
-                        },
-                        "est_pruned": {
-                            "type": "integer"
-                        },
-                        "flows_checked": {
-                            "type": "integer"
-                        },
-                        "flows_notimeout": {
-                            "type": "integer"
-                        },
-                        "flows_removed": {
-                            "type": "integer"
-                        },
-                        "flows_timeout": {
-                            "type": "integer"
-                        },
-                        "new_pruned": {
-                            "type": "integer"
-                        },
-                        "rows_busy": {
-                            "type": "integer"
-                        },
-                        "rows_checked": {
-                            "type": "integer"
-                        },
-                        "rows_empty": {
-                            "type": "integer"
-                        },
-                        "rows_maxlen": {
-                            "type": "integer"
-                        },
-                        "rows_skipped": {
-                            "type": "integer"
-                        }
-                    }
-                },
                 "ftp": {
                     "type": "object",
                     "additionalProperties": false,