[Test] Replace public fun box() with fun box() in all box tests

compiler/testData/codegen/box/regressions/kt5445.kt

@@ -10,7 +10,7 @@ package test2
 
 import test.A
 
-public fun box(): String {
+fun box(): String {
     return B().test(B())
 }
 

compiler/testData/codegen/box/regressions/kt5445_2.kt

@@ -16,7 +16,7 @@ class C : A() {
     }
 }
 
-public fun box(): String {
+fun box(): String {
     return C().a()
 }
 

compiler/testData/codegen/box/regressions/kt864.kt

@@ -11,15 +11,15 @@ fun sample() : Reader {
 World""");
   }
 
-  fun box() : String {
-    // NOTE: Also tested in stdlib: LineIteratorTest.useLines
+fun box() : String {
+  // NOTE: Also tested in stdlib: LineIteratorTest.useLines
 
-    // TODO compiler error
-    // both these expressions causes java.lang.NoClassDefFoundError: collections/CollectionPackage
-    val list1 = sample().useLines { it.toList() }
-    val list2 = sample().useLines<ArrayList<String>>{ it.toCollection(arrayListOf()) }
+  // TODO compiler error
+  // both these expressions causes java.lang.NoClassDefFoundError: collections/CollectionPackage
+  val list1 = sample().useLines { it.toList() }
+  val list2 = sample().useLines<ArrayList<String>>{ it.toCollection(arrayListOf()) }
 
-    if(arrayListOf("Hello", "World") != list1) return "fail"
-    if(arrayListOf("Hello", "World") != list2) return "fail"
-    return "OK"
-  }
+  if(arrayListOf("Hello", "World") != list1) return "fail"
+  if(arrayListOf("Hello", "World") != list2) return "fail"
+  return "OK"
+}