Do not use nightly features

libraries/persistent_store/src/buffer.rs

@@ -310,7 +310,9 @@ impl Storage for BufferStorage {
         // Check and update counters.
         self.incr_page_erases(page);
         // Write to the storage.
-        self.storage[range].fill(0xff);
+        for byte in &mut self.storage[range] {
+            *byte = 0xff;
+        }
         Ok(())
     }
 }

libraries/persistent_store/src/lib.rs

@@ -13,7 +13,6 @@
 // limitations under the License.
 
 #![cfg_attr(not(feature = "std"), no_std)]
-#![feature(slice_fill)]
 
 extern crate alloc;