Remove DiagnosticBuilder::delay_as_bug_without_consuming.

The existing uses are replaced in one of three ways.
- In a function that also has calls to `emit`, just rearrange the code
  so that exactly one of `delay_as_bug` or `emit` is called on every
  path.
- In a function returning a `DiagnosticBuilder`, use
  `downgrade_to_delayed_bug`. That's good enough because it will get
  emitted later anyway.
- In `unclosed_delim_err`, one set of errors is being replaced with
  another set, so just cancel the original errors.

compiler/rustc_parse/src/lexer/mod.rs

@@ -67,7 +67,7 @@ pub(crate) fn parse_token_trees<'a>(
     let (stream, res, unmatched_delims) =
         tokentrees::TokenTreesReader::parse_all_token_trees(string_reader);
     match res {
-        Ok(_open_spacing) if unmatched_delims.is_empty() => Ok(stream),
+        Ok(()) if unmatched_delims.is_empty() => Ok(stream),
         _ => {
             // Return error if there are unmatched delimiters or unclosed delimiters.
             // We emit delimiter mismatch errors first, then emit the unclosing delimiter mismatch