fix(if1): Remove return reference

This closes #153.

exercises/if/if1.rs

@@ -3,7 +3,6 @@
 pub fn bigger(a: i32, b: i32) -> i32 {
     // Complete this function to return the bigger number!
     // Do not use:
-    // - return
     // - another function call
     // - additional variables
     // Scroll down for hints.