fix method signature erased equality (IDEA-57391)

java/java-tests/testData/codeInsight/daemonCodeAnalyzer/genericsHighlighting/IDEA57391.java

@@ -0,0 +1,7 @@
+abstract class B<T> {
+    abstract <S extends T> void foo(T x, S y);
+}
+
+class A extends B<String> {
+    void foo(String x, String y) {}
+}