Split the ast from the parser, remove compiler dep on parser

src/mode.rs

@@ -1,5 +1,3 @@
-use rustpython_parser::parser;
-
 #[derive(Clone, Copy)]
 pub enum Mode {
     Exec,
@@ -19,15 +17,6 @@ impl std::str::FromStr for Mode {
     }
 }
 
-impl Mode {
-    pub fn to_parser_mode(self) -> parser::Mode {
-        match self {
-            Mode::Exec | Mode::Single => parser::Mode::Program,
-            Mode::Eval => parser::Mode::Statement,
-        }
-    }
-}
-
 #[derive(Debug)]
 pub struct ModeParseError {
     _priv: (),