Revert r361148 "[Syntax] Introduce TokenBuffer, start clangToolingSyntax library"

Also reverted r361264 "[Syntax] Rename TokensTest to SyntaxTests. NFC"
which built on it. This is because there were hitting an assert on bots

http://lab.llvm.org:8011/builders/llvm-clang-lld-x86_64-scei-ps4-ubuntu-fast
http://lab.llvm.org:8011/builders/llvm-clang-lld-x86_64-scei-ps4-windows10pro-fast

llvm-svn: 361377