Minor: replace IGNORE_BACKEND with TARGET_BACKEND for the test what should be run only on JVM

The test was written to check the case for Platform Types which now exists only on JVM.

compiler/testData/codegen/box/boxingOptimization/kt19767_3.kt

@@ -1,4 +1,4 @@
-// IGNORE_BACKEND: JS, NATIVE
+// TARGET_BACKEND: JVM
 
 // FILE: M.java
 

js/js.tests/test/org/jetbrains/kotlin/js/test/semantics/JsCodegenBoxTestGenerated.java

@@ -1178,18 +1178,6 @@ public class JsCodegenBoxTestGenerated extends AbstractJsCodegenBoxTest {
             doTest(fileName);
         }
 
-        @TestMetadata("kt19767_3.kt")
-        public void testKt19767_3() throws Exception {
-            String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/codegen/box/boxingOptimization/kt19767_3.kt");
-            try {
-                doTest(fileName);
-            }
-            catch (Throwable ignore) {
-                return;
-            }
-            throw new AssertionError("Looks like this test can be unmuted. Remove IGNORE_BACKEND directive for that.");
-        }
-
         @TestMetadata("kt19767_chain.kt")
         public void testKt19767_chain() throws Exception {
             String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/codegen/box/boxingOptimization/kt19767_chain.kt");