testbed: Remove use of missing log feature (#684)

This code has been here but not used for a long time. There's no
log feature (or dependency) within the testbed crates.

src_testbed/lib.rs

@@ -3,10 +3,6 @@
 
 extern crate nalgebra as na;
 
-#[cfg(feature = "log")]
-#[macro_use]
-extern crate log;
-
 pub use crate::graphics::{BevyMaterial, GraphicsManager};
 pub use crate::harness::plugin::HarnessPlugin;
 pub use crate::physics::PhysicsState;

src_testbed/testbed.rs

@@ -56,7 +56,6 @@ pub enum RunMode {
     Step,
 }
 
-#[cfg(not(feature = "log"))]
 fn usage(exe_name: &str) {
     println!("Usage: {} [OPTION] ", exe_name);
     println!();
@@ -65,15 +64,6 @@ fn usage(exe_name: &str) {
     println!("    --pause - do not start the simulation right away.");
 }
 
-#[cfg(feature = "log")]
-fn usage(exe_name: &str) {
-    info!("Usage: {} [OPTION] ", exe_name);
-    info!("");
-    info!("Options:");
-    info!("    --help  - prints this help message and exits.");
-    info!("    --pause - do not start the simulation right away.");
-}
-
 bitflags::bitflags! {
     #[derive(Copy, Clone, PartialEq, Eq, Debug, Default)]
     pub struct TestbedStateFlags: u32 {