Moved the whole SMT API to a single file. NFC. There is no advantage in having them in separate files, I doubt some will ever use them separately. This also makes it easier to move the API to LLVM. Differential Revision: https://reviews.llvm.org/D54977 llvm-svn: 353372 GitOrigin-RevId: 5f16ad9a1be845fef99155278bc5743e357664cd