Stabilize "file_lock" feature

src/tools/miri/src/lib.rs

@@ -16,7 +16,7 @@
 #![feature(unqualified_local_imports)]
 #![feature(derive_coerce_pointee)]
 #![feature(arbitrary_self_types)]
-#![feature(file_lock)]
+#![cfg_attr(bootstrap, feature(file_lock))]
 // Configure clippy and other lints
 #![allow(
     clippy::collapsible_else_if,

src/tools/miri/tests/pass/shims/fs.rs

@@ -2,7 +2,6 @@
 
 #![feature(io_error_more)]
 #![feature(io_error_uncategorized)]
-#![feature(file_lock)]
 
 use std::collections::BTreeMap;
 use std::ffi::OsString;