Don't steal the parse query when using --pretty

This is the only place aside from the global_ctxt query where it is
stolen.

compiler/rustc_driver_impl/src/pretty.rs

@@ -217,7 +217,7 @@ fn write_or_print(out: &str, sess: &Session) {
 // Extra data for pretty-printing, the form of which depends on what kind of
 // pretty-printing we are doing.
 pub enum PrintExtra<'tcx> {
-    AfterParsing { krate: ast::Crate },
+    AfterParsing { krate: &'tcx ast::Crate },
     NeedsAstMap { tcx: TyCtxt<'tcx> },
 }