Remove LANGUAGE_VERSION from non-coroutine codegen tests

Most of these tests used this directive as a way to opt in to a new
language feature, and most of those features are already stable for a
long time, so no opt-in is needed. Some other tests used the directive
to opt out from a language feature, replace those by the `LANGUAGE`
directive. One test used the directive to test behavior that actually
depended on the API version; use `API_VERSION` directive there instead.

compiler/tests/org/jetbrains/kotlin/codegen/BlackBoxAgainstJavaCodegenTestGenerated.java

@@ -322,9 +322,9 @@ public class BlackBoxAgainstJavaCodegenTestGenerated extends AbstractBlackBoxAga
             runTest("compiler/testData/codegen/boxAgainstJava/ieee754/explicitEqualsCall.kt");
         }
 
-        @TestMetadata("explicitEqualsCall_lv12.kt")
-        public void testExplicitEqualsCall_lv12() throws Exception {
-            runTest("compiler/testData/codegen/boxAgainstJava/ieee754/explicitEqualsCall_lv12.kt");
+        @TestMetadata("explicitEqualsCallNull.kt")
+        public void testExplicitEqualsCallNull() throws Exception {
+            runTest("compiler/testData/codegen/boxAgainstJava/ieee754/explicitEqualsCallNull.kt");
         }
 
         @TestMetadata("float.kt")