Comment string tweaks:

* Merge two strings about an invalid comment ID.
* Add missing context to 'Mark as Spam' string.
* Merge two 'In Response To' strings, replace redundant context with a translator comment.

props pavelevap.
fixes #32334.
Built from https://develop.svn.wordpress.org/trunk@33436


git-svn-id: http://core.svn.wordpress.org/trunk@33403 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-admin/includes/class-wp-comments-list-table.php

@@ -357,8 +357,10 @@ class WP_Comments_List_Table extends WP_List_Table {
 		$columns['author'] = __( 'Author' );
 		$columns['comment'] = _x( 'Comment', 'column name' );
 
-		if ( !$post_id )
-			$columns['response'] = _x( 'In Response To', 'column name' );
+		if ( ! $post_id ) {
+			/* translators: column name or table row header */
+			$columns['response'] = __( 'In Response To' );
+		}
 
 		return $columns;
 	}