remove unused ftl

Author: AndyJado

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

@@ -135,6 +135,3 @@ borrowck_perhaps_save_in_new_local_to_drop =
 
 borrowck_outlive_constraint_need_borrow_for =
     {$category}requires that `{$desc}` is borrowed for `{$region_name}`
-
-borrowck_outlive_constraint_need_borrow_lasts =
-    {$category}requires that `{$borrow_desc}` lasts for `{$region_name}`