Remove package objects (#244)

- Deprecated in scala 3

src/main/scala/introcourse/level03/package.scala

@@ -1,11 +1,7 @@
-package introcourse
+package introcourse.level03
 
-package object level03 {
-
-  case class Person(name: String, age: Int)
-
-  enum TrafficLight {
-    case Red, Yellow, Green
-  }
+case class Person(name: String, age: Int)
 
+enum TrafficLight {
+  case Red, Yellow, Green
 }

src/main/scala/introcourse/level04/package.scala

@@ -1,11 +1,7 @@
-package introcourse
+package introcourse.level04
 
-package object level04 {
-
-  case class Person(name: String, age: Int)
-
-  enum TrafficLight {
-    case Red, Yellow, Green
-  }
+case class Person(name: String, age: Int)
 
+enum TrafficLight {
+  case Red, Yellow, Green
 }

src/main/scala/introcourse/level05/package.scala

@@ -1,7 +1,3 @@
-package introcourse
+package introcourse.level05
 
-package object level05 {
-
-  case class Person(name: String, age: Int)
-
-}
+case class Person(name: String, age: Int)