replace explicit SSL package lists by "tls" feature

This fixes the build failures ("file-system partition too big") for Archer
C6 v2 and C60 v1. Apparently Gluon now just uses the already-installed
mbedtls SSL implementation, so we save the space of libustream-openssl.
The "tls" feature had been added in Gluon 2023.2.

image-customization.lua

@@ -32,11 +32,7 @@ packages({
 if not device_class('tiny') then
   features({
     'wireless-encryption-wpa3',
-  })
-  packages({
-    'ca-bundle',
-    'ca-certificates',
-    'libustream-openssl',
+    'tls'
   })
 end