Update de_web_plugin.cpp
Update de_web_plugin.cpp

- Stop polling the gateway device.
- Use Zigbee epoch for time sync, as deCONZ code v2.05.80 now handles `utc` correctly.

dresden-elektronik/deconz-rest-plugin,dresden-elektronik/deconz-rest-plugin,dresden-elektronik/deconz-rest-plugin,dresden-elektronik/deconz-rest-plugin,dresden-elektronik/deconz-rest-plugin