libstd/sys/redox/os.rs: unused static variable

https://github.com/rust-lang/rust/blob/master/src/libstd/sys/redox/os.rs#L33

```rust
const TMPBUF_SZ: usize = 128;
static ENV_LOCK: Mutex = Mutex::new();
```

Could anybody confirm if they can safely be removed?  It looks like they were copy-and-pasted from `unix/os.rs` but I'm not familiar with Redox.