Silence some unused import warnings

Author: alexcrichton

src/libstd/num/f32.rs

@@ -867,7 +867,6 @@ impl num::FromStrRadix for f32 {
 #[cfg(test)]
 mod tests {
     use f32::*;
-    use prelude::*;
 
     use num::*;
     use num;

src/libstd/num/f64.rs

@@ -869,7 +869,6 @@ impl num::FromStrRadix for f64 {
 #[cfg(test)]
 mod tests {
     use f64::*;
-    use prelude::*;
 
     use num::*;
     use num;

src/libstd/task.rs

@@ -65,7 +65,6 @@ use rt::task::Task;
 use str::{Str, SendStr, IntoMaybeOwned};
 
 #[cfg(test)] use any::{AnyOwnExt, AnyRefExt};
-#[cfg(test)] use ptr;
 #[cfg(test)] use result;
 
 /// Indicates the manner in which a task exited.