Docs: Fixed some deleted refs

docs/reference/migration/migrate_1_0.asciidoc

@@ -350,9 +350,9 @@ in the query string.
 * The `field` query has been removed.  Use the
   <<query-dsl-query-string-query,`query_string`>> query instead.
 
-* Per-document boosting with the <<mapping-boost-field,`_boost`>> field has
+* Per-document boosting with the `_boost` field has
   been removed.  You can use the
-  <<function-score-instead-of-boost,`function_score`>> instead.
+  <<query-dsl-function-score-query,`function_score`>> instead.
 
 * The `path` parameter in mappings has been deprecated. Use the
   <<copy-to,`copy_to`>> parameter instead.