Remove projects/sample.

As an example that was not actually being used, it suffered from a slow bitrot.

The two main issues with it were that it had no cmake support and
included a copy of the autoconf directory. The reality is that
autoconf is not easily composable. The lack of composabilty is why we
have clang options in llvm's configure. Suggesting that users include
a copy of autoconf/ in their projects seems a bad idea.

We are also in the process of switching to cmake, so pushing autoconf
to new project is probably not what we want.