Remove unneeded asserts from JavaSupertypeResolver

Don't do anything special if a Java class happens to extend jet.JetObject: it's
not a Kotlin class and we should collect all its supertypes correctly

compiler/testData/loadJava/sourceJava/ClassExtendsTypeParameter.java

@@ -0,0 +1,4 @@
+package test;
+
+public class ClassExtendsTypeParameter<T> extends T {
+}

compiler/testData/loadJava/sourceJava/ClassExtendsTypeParameter.txt

@@ -0,0 +1,5 @@
+package test
+
+public open class ClassExtendsTypeParameter</*0*/ T> : T {
+    public constructor ClassExtendsTypeParameter</*0*/ T>()
+}