Disabling "check for updates" should fully disable checking for boards or libraries against the server

Given [this](https://github.com/arduino/Arduino/issues/8988) issue, unticking "check for updates **at** startup" should disable any check against the server(s). There's absolutely no need to call upon a url for the boards or libraries since _you already berelinquish being notified of any updates at all_.

The [fix](https://github.com/arduino/Arduino/pull/9023) is kind of a joke, I mean, really, no one is going to change variants, or the compiler for a microcontroller, or a serious library, in four hours. These should actually be released with point releases such as Arduino 1.x.x etc.

Start by reading issue #8988 and pull request #9023 to understand the existing startup update preference and current behavior. Trace the Arduino IDE 1.x update checks for boards and libraries, then verify that unticking the preference prevents requests to update servers while preserving the intended startup behavior.

Written by the indexing model from the issue text.