Fix warnings in preparation for Rust 1.54.0

This CL fixes several new warnings generated by rustc 1.54.0.

Bug: 194812675
Test: m rust
Change-Id: I3076313ea51c6f4e74029ad9fb45d6f0b6dea460
diff --git a/keystore2/src/id_rotation.rs b/keystore2/src/id_rotation.rs
index dbf0fc9..e3992d8 100644
--- a/keystore2/src/id_rotation.rs
+++ b/keystore2/src/id_rotation.rs
@@ -27,7 +27,7 @@
 use std::time::Duration;
 
 const ID_ROTATION_PERIOD: Duration = Duration::from_secs(30 * 24 * 60 * 60); // Thirty days.
-static TIMESTAMP_FILE_NAME: &str = &"timestamp";
+static TIMESTAMP_FILE_NAME: &str = "timestamp";
 
 /// The IdRotationState stores the path to the timestamp file for deferred usage. The data
 /// partition is usually not available when Keystore 2.0 starts up. So this object is created
@@ -83,7 +83,7 @@
     fn test_had_factory_reset_since_id_rotation() -> Result<()> {
         let temp_dir = TempDir::new("test_had_factory_reset_since_id_rotation_")
             .expect("Failed to create temp dir.");
-        let id_rotation_state = IdRotationState::new(&temp_dir.path());
+        let id_rotation_state = IdRotationState::new(temp_dir.path());
 
         let mut temp_file_path = temp_dir.path().to_owned();
         temp_file_path.push(TIMESTAMP_FILE_NAME);