fix removing devices

src/emsesp.cpp

@@ -83,8 +83,7 @@ void EMSESP::fetch_device_values(const uint8_t device_id) {
 
 // clears list of recognized devices
 void EMSESP::clear_all_devices() {
-    // emsdevices.clear(); // or use empty to release memory too
-    emsdevices.empty();
+    emsdevices.clear(); // remove entries, but doesn't delete actual devices
 }
 
 // return number of devices of a known type