Remove outdated comment (#2957)

* Remove comment mentioning another class (`AbstractIterableTest`) that
does not exist

Author: bvkatwijk

vavr/src/test/java/io/vavr/IterableTest.java

@@ -29,7 +29,6 @@
 
 import static org.assertj.core.api.Assertions.assertThat;
 
-// Specific tests. For general tests, see AbstractIterableTest.
 public class IterableTest {
 
     // -- eq