[ES9618XX] Use platform.json for ASIC sensor polling configuration

With the enhancement introduced in PR sonic-net#20826 -
"[asic_sensors] Generate the ASIC sensor polling configuration
based on the platform.json" - we can now define ASIC sensor polling
settings directly in platform.json.

This change removes the need for a custom.json override and simplifies
platform-specific configuration by centralizing the polling interval
and status settings under platform.json.

Signed-off-by: Michael Zaidman <[email protected]>

Author: MichaelZaidman

device/accton/x86_64-accton_es9618xx-r0/custom.json

@@ -683,5 +683,9 @@
             "8x100G": ["Eth16/1", "Eth16/2", "Eth16/3", "Eth16/4", "Eth16/5", "Eth16/6", "Eth16/7", "Eth16/8"]
         }
     }
+  },
+  "asic_sensors": {
+        "poll_interval": "10",
+        "poll_admin_status": "enable"
   }
 }

device/accton/x86_64-accton_es9618xx-r0/platform.json

@@ -20,16 +20,6 @@ XSIGHT_PCI_ID=""
 XSIGHT_DEVICE=""
 FIRSTBOOT="/tmp/notify_firstboot_to_platform"
 
-if [ -f $FIRSTBOOT ]; then
-    PLATFORM=$(sed -n 's/onie_platform=\(.*\)/\1/p' /host/machine.conf)
-
-    # update default config from custom.json
-    if [ -f /usr/share/sonic/device/$PLATFORM/custom.json ]; then
-        sonic-cfggen --from-db -j /usr/share/sonic/device/$PLATFORM/custom.json --print-data > /etc/sonic/config_db.json
-        sonic-cfggen -j /usr/share/sonic/device/$PLATFORM/custom.json --write-to-db
-    fi
-fi
-
 fname=$(basename $0)
 
 # The eth0 interface intermittently disappears on reboot.