chore(tazjin/rlox): Move other modules under treewalk::

It's unclear if the second part of the book can reuse anything from
the first part (I'm guessing probably the scanner, but I'll move that
back if it turns out to be the case).

Change-Id: I9411355929e31ac6e953599e51665406b1f48d55
Reviewed-on: https://cl.tvl.fyi/c/depot/+/2415
Reviewed-by: tazjin <mail@tazj.in>
Tested-by: BuildkiteCI

users/tazjin/rlox/src/main.rs

@@ -5,9 +5,6 @@ use std::io::Write;
 use std::process;
 
 mod bytecode;
-mod errors;
-mod parser;
-mod scanner;
 mod treewalk;
 
 fn main() {
@@ -16,9 +13,3 @@ fn main() {
         _ => bytecode::main(),
     }
 }
-
-fn report_errors(errors: Vec<errors::Error>) {
-    for error in errors {
-        errors::report(&error);
-    }
-}