Xcode 11 doesn't support anything below iOS 7.0 (the linker will automatically
change the deployment target to 7.0), so we need to drop support as well
(since our native bits will be targetting iOS 7.0, and we can't change that).
https://github.com/xamarin/xamarin-macios/issues/6213
The change is a pre step to fix https://github.com/xamarin/xamarin-macios/issues/6162
We are removing the not longer child directory bcl-test/BCLTests since
there is not longer any reason for it to exist. The changes make sure
that the tests work as expected in the new directory.
Next step, move all the test apps to their own directory.