merge diagnostics about incorrect uses of .await

Author: pvdrz

compiler/rustc_error_messages/locales/en-US/parser.ftl

@@ -26,9 +26,5 @@ parser-incorrect-semicolon =
 
 parser-incorrect-use-of-await =
     incorrect use of `await`
-    .suggestion = `await` is not a method call, remove the parentheses
-
-
-parser-incorrect-await =
-    incorrect use of `await`
-    .suggestion = `await` is a postfix operation
+    .parentheses-suggestion = `await` is not a method call, remove the parentheses
+    .postfix-suggestion = `await` is a postfix operation

compiler/rustc_parse/src/parser/diagnostics.rs

@@ -310,16 +310,16 @@ struct IncorrectSemicolon<'a> {
 #[error(slug = "parser-incorrect-use-of-await")]
 struct IncorrectUseOfAwait {
     #[primary_span]
-    #[suggestion(applicability = "machine-applicable")]
+    #[suggestion(message = "parentheses-suggestion", applicability = "machine-applicable")]
     span: Span,
 }
 
 #[derive(SessionDiagnostic)]
-#[error(slug = "parser-incorrect-await")]
+#[error(slug = "parser-incorrect-use-of-await")]
 struct IncorrectAwait {
     #[primary_span]
     span: Span,
-    #[suggestion(code = "{expr}.await{question_mark}")]
+    #[suggestion(message = "postfix-suggestion", code = "{expr}.await{question_mark}")]
     sugg_span: (Span, Applicability),
     expr: String,
     question_mark: &'static str,