removed legacy apple tools (but new ones need to be modernized yet)

[memsharded]

Basically, replacing the legacy tools.apple... with conan.tools.apple and some other minor changes:

• Tools not made public yet, the UIs need to be revised against real-life use cases and ConanCenter.
• Now, XCRun is going to be used only for testing purposes.
• Removing the sdk=None value for all the Apple OSs from settings.yml. For instance:

    Macos:
           version: [None, "10.6", "10.7", "10.8", "10.9", "10.10", "10.11", "10.12", "10.13", "10.14", "10.15", "11.0", "12.0", "13.0"]
       iOS:
           sdk: ["iphoneos", "iphonesimulator"]
   . . .
  

Now it must be explicitly written in the user profiles via os.sdk (except for Macos because it's automatically put as macosx).

• Simplified and refactored functions like apple_min_version_flag().

[memsharded]

LGTM!