remove strange file and print source in codegen test

lang/src/test.m

@@ -1 +0,0 @@
-let fn if

lang/tests/codegen.rs

@@ -66,6 +66,7 @@ fn main() {
                 nodes: util::vec::Vec::new(),
             };
             let expr_id = parser(&mut ast);
+            eprintln!("{}", core::str::from_utf8_unchecked(src));
             eprintln!("Parsed expression ID: {}", expr_id);
             let mut symtable = core::mem::MaybeUninit::<util::defs::SymbolTable>::uninit();
             util::defs::ast_build_symtable(&mut ast, expr_id, &mut symtable);