Remove unnecessary lifetime from FeaturePreviouslyDeclared.

Author: nnethercote

compiler/rustc_passes/src/errors.rs

@@ -1012,12 +1012,12 @@ pub(crate) struct FeatureStableTwice {
 
 #[derive(Diagnostic)]
 #[diag(passes_feature_previously_declared, code = E0711)]
-pub(crate) struct FeaturePreviouslyDeclared<'a, 'b> {
+pub(crate) struct FeaturePreviouslyDeclared<'a> {
     #[primary_span]
     pub span: Span,
     pub feature: Symbol,
     pub declared: &'a str,
-    pub prev_declared: &'b str,
+    pub prev_declared: &'a str,
 }
 
 pub(crate) struct BreakNonLoop<'a> {