Remove the old parser bits

Now that everything has been migrated to the new AST, remove as much of
the parse_tree bits as possible

src/parser.cpp

@@ -26,7 +26,6 @@
 #include "proc.h"
 #include "reader.h"
 #include "sanity.h"
-#include "tnode.h"
 #include "wutil.h"  // IWYU pragma: keep
 
 class io_chain_t;