Revert "Add to the README.md that when checking out llvm/clang from s…

…wift-{llvm,clang}, one needs to checkout the stable branches."

This reverts commit f7a29c7.

This is actually not necessary. I forgot that the default branch for
apple-{llvm/clang} is stable. Sorry for the noise!

README.md

@@ -65,14 +65,13 @@ with version 2 shipped with Ubuntu.
 
       git clone [email protected]:/apple/swift.git swift
       git clone [email protected]:/apple/swift-llvm.git llvm
-      (cd llvm && git checkout -t origin/stable)
       git clone [email protected]:/apple/swift-clang.git clang
-      (cd clang && git checkout -t origin/stable)
       git clone [email protected]:/apple/swift-lldb.git lldb
       git clone [email protected]:/apple/swift-cmark.git cmark
       git clone [email protected]:/apple/swift-llbuild.git llbuild
       git clone [email protected]:/apple/swift-package-manager.git swiftpm
 
+
 ### Building Swift
 
     swift/utils/build-script -t