Fix compileJavaAgainstKotlin tests

- Use another API to get file name out of a javac diagnostic
  (.getSource().getName()'s behavior changed in JDK 8)
- Delete .txt files for those tests which check that javac reported a
  compilation error; the order and content of declarations in those
  files is undefined

compiler/testData/compileJavaAgainstKotlin/sealed/Derived.txt

@@ -1,13 +0,0 @@
-package test
-
-public sealed class Season {
-    private constructor Season()
-
-    public final class Cold : test.Season {
-        public constructor Cold()
-    }
-
-    public final class Warm : test.Season {
-        public constructor Warm()
-    }
-}

compiler/testData/compileJavaAgainstKotlin/sealed/Instance.txt

@@ -1,13 +0,0 @@
-package test
-
-public sealed class Season {
-    private constructor Season()
-
-    public final class Cold : test.Season {
-        public constructor Cold()
-    }
-
-    public final class Warm : test.Season {
-        public constructor Warm()
-    }
-}