Remove unneeded pub

exercises/17_tests/tests4.rs

@@ -7,7 +7,7 @@ struct Rectangle {
 
 impl Rectangle {
     // Only change the test functions themselves
-    pub fn new(width: i32, height: i32) -> Self {
+    fn new(width: i32, height: i32) -> Self {
         if width <= 0 || height <= 0 {
             panic!("Rectangle width and height cannot be negative!")
         }