Clean up and unify exercises

exercises/03_if/if1.rs

@@ -1,7 +1,3 @@
-// if1.rs
-//
-// Execute `rustlings hint if1` or use the `hint` watch subcommand for a hint.
-
 pub fn bigger(a: i32, b: i32) -> i32 {
     // Complete this function to return the bigger number!
     // If both numbers are equal, any of them can be returned.

exercises/03_if/if2.rs

@@ -1,9 +1,5 @@
-// if2.rs
-//
 // Step 1: Make me compile!
 // Step 2: Get the bar_for_fuzz and default_to_baz tests passing!
-//
-// Execute `rustlings hint if2` or use the `hint` watch subcommand for a hint.
 
 pub fn foo_if_fizz(fizzish: &str) -> &str {
     if fizzish == "fizz" {

exercises/03_if/if3.rs

@@ -1,7 +1,3 @@
-// if3.rs
-//
-// Execute `rustlings hint if3` or use the `hint` watch subcommand for a hint.
-
 pub fn animal_habitat(animal: &str) -> &'static str {
     let identifier = if animal == "crab" {
         1