Exclude vm2 from CMake build for now.

It doesn't build. We can add it back when it does.

Closes #296

COPYBARA_INTEGRATE_REVIEW=https://github.com/google/iree/pull/296 from GMNGeoffrey:cmake e22cedbde109bffc3f71eeed59c8129c4f81a113
PiperOrigin-RevId: 287352338
diff --git a/CMakeLists.txt b/CMakeLists.txt
index b2e953e..f71ec76 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -105,7 +105,6 @@
 add_subdirectory(iree/rt)
 add_subdirectory(iree/schemas)
 add_subdirectory(iree/vm)
-add_subdirectory(iree/vm2)
 
 if(${IREE_BUILD_COMPILER})
   add_subdirectory(third_party/glslang EXCLUDE_FROM_ALL)