[xcode] Eliminate the llbuild-all-in-one target, which never worked well.
[xcode] Eliminate the llbuild-all-in-one target, which never worked well.

 - Hopefully real support for static library code coverage is coming soon...

apple/swift-llbuild,apple/swift-llbuild,apple/swift-llbuild,apple/swift-llbuild,apple/swift-llbuild,apple/swift-llbuild,apple/swift-llbuild