Carve out Ada selftests in alr to its own Ada testsuite

[mosteo]

Take advantage of the new alr test to remove test code from Alire itself.

Incidentally, I think the test named Assertions_Enabled would make for a better default test instead of the empty example we are generating now. This one will likely be left in by most people as it guarantees the testsuite is build in validation mode, whereas the current example requires removal or renaming and does nothing useful.

PR creation checklist

• A test is included, if required by the changes.