Get rid of CompileKotlinAgainstMultifileKotlinTestGenerated and boxMultifileClasses/

Merge tests in boxMultifileClasses/calls to one test case; copy the two
resulting tests (+ change box to main) to compileKotlinAgainstKotlin

compiler/testData/codegen/boxMultiFile/constPropertyReferenceFromMultifileClass.kt

@@ -0,0 +1,26 @@
+// FILE: 1.kt
+
+import a.OK
+
+fun box(): String {
+    val okRef = ::OK
+
+    // TODO: see KT-10892
+//    val annotations = okRef.annotations
+//    val numAnnotations = annotations.size
+//    if (numAnnotations != 1) {
+//        return "Failed, annotations: $annotations"
+//    }
+
+    return okRef.get()
+}
+
+// FILE: 2.kt
+
+@file:[JvmName("MultifileClass") JvmMultifileClass]
+package a
+
+annotation class A
+
+@A
+const val OK: String = "OK"