McuSupportPlugin: remove support for deprecated versions of the SDK

The current official SDK version for QtForMcus is 2.0

The QtCreator plugin still contains workarounds and hacks for 1.x versions. Currently down to 1.3 is supported.

Many of those involve hardcoded information in the plugin that is activated when some expected piece of data is not present in the json. For example: if some particular environment variable is not explicitly referenced in the json, the plugin assumes something about the target platform and proceeds to create that thing. Which causes many false positives when features are deprecated in newer versions of the SDK, like all environment variables going away for example.

• Version 1.3: returned by minimalQulVersion()

• Version 1.3 and sooner: triggers "createDesktopTargetsLegacy" and "createMcuTargetsLegacy" in McuTargetFactory

• Version 1.8 and later: extracts toolchain Versions from the json kit description (used for version detection)

• Version 2.0 or later: checked in "expectsCmakeVars"

• Version 1.7 or later: skips adding clang to system PATH when creating kit
• Version 1.3 or sooner: adds FreRTOS cmake variable to kit, and to kit name
• Version 2.x or later: parsing kit descriptions
• Version below 1.5: location of the fallback desktop libraries when json kits are present but not for desktop
• Version 1.7 or later: Used in the CMake template by the wizard, for supporting the older API (which was renamed in 1.7).

• oldSdkQtcRequiredVersion should go into its own file/class. It's used to display to the user a suggestion for older versions of QtCreator that can support older SDKs.