Extremely minor fixes

Only doing this to remedy a very minor annoyance of mine. These are not major (or even very helpful) changes by any measure.

- Removes an unneeded `use` statement
- Fixes a [deprecated](https://doc.rust-lang.org/nightly/edition-guide/rust-2021/panic-macro-consistency.html) use of `panic!`

demo/native/src/main.rs

@@ -26,7 +26,6 @@ use pathfinder_resources::ResourceLoader;
 use pathfinder_resources::fs::FilesystemResourceLoader;
 use std::cell::Cell;
 use std::collections::VecDeque;
-use std::mem;
 use std::path::PathBuf;
 use std::sync::Mutex;
 use surfman::{SurfaceAccess, SurfaceType, declare_surfman};
@@ -163,7 +162,7 @@ impl Window for WindowImpl {
     fn metal_device(&self) -> metal::Device {
         // FIXME(pcwalton): Remove once `surfman` upgrades `metal-rs` version.
         unsafe {
-            mem::transmute(self.metal_device.0.clone())
+            std::mem::transmute(self.metal_device.0.clone())
         }
     }
 

examples/swf_basic/src/main.rs

@@ -36,7 +36,7 @@ fn main() {
             Ok(bytes) => {
                 swf_bytes = bytes;
             },
-            Err(e) => panic!(e)
+            Err(e) => panic!("{}", e)
         }
     } else {
         // NOTE(jon): This is a version of the ghostscript tiger graphic flattened to a single