[QoS] Remove config keys for pfc and pfcwd on service ports (#24148)

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Remove config keys for pfc and pfcwd on service ports
#### Why I did it
By setting the keys to an empty string "" for `pfcwd_sw_enable`, the buffermgrd still creates corresponding entries in the `PFC_WD` table. This in turn misleads the pfcwd orch to check for TCs where PFCWD is enabled on those service ports which it cannot find since it's an empty string resulting in this constant error stream:

```
2025 Sep 27 12:56:29.631650 str5-7060x6-moby-512-2 NOTICE swss#orchagent: :- registerInWdDb: No lossless TC found on port Ethernet512
2025 Sep 27 12:56:29.631650 str5-7060x6-moby-512-2 ERR swss#orchagent: :- createEntry: Failed to start PFC Watchdog on port Ethernet512
2025 Sep 27 12:56:29.631650 str5-7060x6-moby-512-2 NOTICE swss#orchagent: :- registerInWdDb: No lossless TC found on port Ethernet513
2025 Sep 27 12:56:29.631680 str5-7060x6-moby-512-2 ERR swss#orchagent: :- createEntry: Failed to start PFC Watchdog on port Ethernet513
2025 Sep 27 12:56:29.969523 str5-7060x6-moby-512-2 NOTICE swss#orchagent: :- registerInWdDb: No lossless TC found on port Ethernet512
2025 Sep 27 12:56:29.969523 str5-7060x6-moby-512-2 ERR swss#orchagent: :- createEntry: Failed to start PFC Watchdog on port Ethernet512
2025 Sep 27 12:56:29.969523 str5-7060x6-moby-512-2 NOTICE swss#orchagent: :- registerInWdDb: No lossless TC found on port Ethernet513
2025 Sep 27 12:56:29.969523 str5-7060x6-moby-512-2 ERR swss#orchagent: :- createEntry: Failed to start PFC Watchdog on port Ethernet513
```

Fix here is to completely remove the key config to prevent buffermgrd in creating PFCWD entries for those service ports.

Issue was not found earlier since the error messages take about 15 minutes to show up from a reload.

##### Work item tracking
- Microsoft ADO **(number only)**:

#### How I did it

#### How to verify it

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Completely remove config keys for pfc and pfcwd on service ports
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Author: mssonicbld

files/build_templates/qos_config.j2

@@ -445,10 +445,7 @@
 {% endif %}
 {% endif %}
 {% if port not in PORT_DPC %}
-{% if port in PORT_SERVICE %}
-            "pfc_enable"      : "",
-            "pfcwd_sw_enable" : "",
-{% else %}
+{% if port not in PORT_SERVICE %}
 {% if port in port_names_list_extra_queues %}
             "pfc_enable"      : "2,3,4,6",
 {% else %}

src/sonic-config-engine/tests/sample_output/py3/qos-arista7060x6.json

@@ -1156,16 +1156,12 @@
         "Ethernet512": {
             "dscp_to_tc_map"  : "AZURE",
             "tc_to_queue_map" : "AZURE",
-            "pfc_enable"      : "",
-            "pfcwd_sw_enable" : "",
             "tc_to_pg_map"    : "AZURE",
             "pfc_to_queue_map": ""
         },
         "Ethernet513": {
             "dscp_to_tc_map"  : "AZURE",
             "tc_to_queue_map" : "AZURE",
-            "pfc_enable"      : "",
-            "pfcwd_sw_enable" : "",
             "tc_to_pg_map"    : "AZURE",
             "pfc_to_queue_map": ""
         }