* remove migrated documentation
All of these are present now on our https://devices.esphome.io/ site.
The missing ones were pushed with https://github.com/esphome/esphome-devices/pull/385, and the rest ones were already in, thus removing here the duplicates.
* Update modbus.rst
* Update modbus.rst
* Update modbus_controller.rst
* Update ltr390.rst
* Update ltr390.rst
* Update modbus_controller.rst
* fix broken links
* Update index.rst
* Update index.rst
In the example `i` gets incremented before the loop is over, but it is referenced again.
This can cause unexpected resutls if just blindly copy this example. (ask me, how i know :)
