Update travis config so NOZZLE_CLEAN_FEATURE no longer depends on AUTO_BED_LEVELING_FEATURE

.travis.yml

   # Test NOZZLE_CLEAN_FEATURE
   #
   - restore_configs
-  - opt_enable AUTO_BED_LEVELING_FEATURE NOZZLE_CLEAN_FEATURE FIX_MOUNTED_PROBE
+  - opt_enable NOZZLE_CLEAN_FEATURE
   - build_marlin
   #
   #