remove some leftover //ignore that did not do anything

Author: RalfJung

tests/pass/foreign-fn-linkname.rs

@@ -1,5 +1,3 @@
-//ignore-windows: Uses POSIX APIs
-
 use std::ffi::CString;
 
 mod mlibc {

tests/pass/regions-mock-trans.rs

@@ -1,5 +1,3 @@
-//ignore-windows: Uses POSIX APIs
-
 use std::mem;
 
 struct Arena(());