Move some functions from rustc_expand to rustc_builtin_macros.

These functions are only used in `rustc_builtin_macros`, so it makes
sense for them to live there. This allows them to be changed from `pub`
to `pub(crate)`.

compiler/rustc_expand/src/errors.rs

@@ -152,29 +152,6 @@ pub(crate) struct HelperAttributeNameInvalid {
     pub name: Ident,
 }
 
-#[derive(Diagnostic)]
-#[diag(expand_expected_comma_in_list)]
-pub(crate) struct ExpectedCommaInList {
-    #[primary_span]
-    pub span: Span,
-}
-
-#[derive(Diagnostic)]
-#[diag(expand_only_one_argument)]
-pub(crate) struct OnlyOneArgument<'a> {
-    #[primary_span]
-    pub span: Span,
-    pub name: &'a str,
-}
-
-#[derive(Diagnostic)]
-#[diag(expand_takes_no_arguments)]
-pub(crate) struct TakesNoArguments<'a> {
-    #[primary_span]
-    pub span: Span,
-    pub name: &'a str,
-}
-
 #[derive(Diagnostic)]
 #[diag(expand_feature_removed, code = E0557)]
 pub(crate) struct FeatureRemoved<'a> {