Drop libSyntax's Unit Tests

We no longer intend to support the libSyntax AST, so let's drop
the tests that are only going to get in the way of us iterating
on the Swift Syntax tree.

Author: CodaFi

unittests/CMakeLists.txt

@@ -17,11 +17,7 @@ if(SWIFT_INCLUDE_TOOLS)
   add_subdirectory(Sema)
   add_subdirectory(SIL)
   add_subdirectory(SwiftDemangle)
-  add_subdirectory(Syntax)
 
-  if(SWIFT_BUILD_SYNTAXPARSERLIB)
-    add_subdirectory(SyntaxParser)
-  endif()
   add_subdirectory(Threading)
 
   if(SWIFT_BUILD_SDK_OVERLAY)