Update comments

Author: noti0na1

tests/explicit-nulls/neg/eq.scala

@@ -41,4 +41,4 @@ class Foo {
   null == false // error
   'a' == null   // error
   null == 'b'   // error
-}
+}

tests/explicit-nulls/pos/flow4.scala

@@ -1,4 +1,3 @@
-// TODO: broken
 // This test is based on tests/pos/rbtree.scala
 // and it tests that we can use an inline method to "abstract" a more complicated
 // isInstanceOf check, while at the same time getting the flow inference to know

tests/explicit-nulls/pos/stable-path.scala

@@ -8,4 +8,4 @@ def f() = {
   val a: xs.x.type = xs.x
   assert(xs.next != null)
   val b: xs.next.x.type = xs.next.x
-}
+}

tests/explicit-nulls/pos/while-loop.scala

@@ -15,4 +15,4 @@ def f = {
     }
     xs = xs.next
   }
-}
+}

tests/explicit-nulls/run/while-loop.scala

@@ -9,4 +9,4 @@ object Test {
       xs = xs.next
     }
   }
-}
+}