McuSupport: remove cmake mapper

Starting with Qt For MCUs 2.0, environment variables are not
used to track dependencies any more, but cmake variables are.
Due to time constraints, we implemented a env-to-cmake mapper
to cover that gap at the moment. This patch removes that hack
and implements tracking dependencies through cmake variables.

Task-number: QTCREATORBUG-26904
Change-Id: Id8553a764d212d9b12e4adc54fc56233bfeb9a5b
Reviewed-by: <github-actions-qt-creator@cristianadam.eu>
Reviewed-by: Alessandro Portale <alessandro.portale@qt.io>

src/plugins/mcusupport/mcusupportplugin.cpp

@@ -125,6 +125,7 @@ void McuSupportPlugin::askUserAboutMcuSupportKitsSetup()
                              tr("Create Kits for Qt for MCUs? "
                                 "To do it later, select Options > Devices > MCU."),
                              Utils::InfoBarEntry::GlobalSuppression::Enabled);
+    // clazy:excludeall=connect-3arg-lambda
     info.addCustomButton(tr("Create Kits for Qt for MCUs"), [setupMcuSupportKits] {
         ICore::infoBar()->removeInfo(setupMcuSupportKits);
         QTimer::singleShot(0, []() { ICore::showOptionsDialog(Constants::SETTINGS_ID); });