edge-core: no longer force port 443 by default

Now that edge-core can connect to Pelion through an upstream proxy,
we no longer need to force it to connect over port 443 by default.

The build option and patches for port 443 still exist, so just set
the flag back to true to turn port 443 override back on again.

snap/snapcraft.yaml

@@ -238,7 +238,7 @@ parts:
         - cmake
         - git
       build-environment:
-        - COAP_PORT_OVERRIDE_443: "true"
+        - COAP_PORT_OVERRIDE_443: "false"
       override-pull: |
         snapcraftctl pull
         # mbed_cloud_dev_credentials.c is required if DEVELOPER_MODE=ON