restrict BLE example only build BLE_LED

Author: Qinghao Shi

tools/test/examples/examples_cmake.json

@@ -118,16 +118,8 @@
       "github":"https://github.com/ARMmbed/mbed-os-example-ble",
       "sub-repo-example": true,
       "subs": [
-            "BLE_BatteryLevel",
-            "BLE_GAP",
-            "BLE_GattClient",
-            "BLE_GattServer",
-            "BLE_HeartRate",
-            "BLE_LED",
-            "BLE_LEDBlinker",
-            "BLE_PeriodicAdvertising",
-            "BLE_Privacy",
-            "BLE_SM"
+            "BLE_LED"
+
       ],
       "features" : [],
       "targets" : ["NRF52840_DK", "DISCO_L475VG_IOT01A"],