Revert 374882 "[Concepts] Concept Specialization Expressions" This reverts commit ec87b003823d63f3342cf648f55a134c1522e612. The test fails on Windows, see e.g. http://lab.llvm.org:8011/builders/clang-x64-windows-msvc/builds/11533/steps/stage%201%20check/logs/stdio Also revert follow-up r374893. git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@374899 91177308-0d34-0410-b5e6-96231b3b80d8