Remove stale comments about @NonNull annotations in the JDK.

Our nullness checking has seen `@NonNull` annotations in the JDK since cl/648064454.

RELNOTES=n/a
PiperOrigin-RevId: 672970833

guava/src/com/google/common/collect/Maps.java

@@ -1770,11 +1770,6 @@ public V computeIfAbsent(
 
     @Override
     @CheckForNull
-    /*
-     * Our checker arguably should produce a nullness error here until we see @NonNull in JDK APIs.
-     * But it doesn't, which may be a sign that we still permit parameter contravariance in some
-     * cases?
-     */
     public V computeIfPresent(
         K key, BiFunction<? super K, ? super @NonNull V, ? extends @Nullable V> remappingFunction) {
       throw new UnsupportedOperationException();
@@ -3686,17 +3681,8 @@ public V computeIfAbsent(
       throw new UnsupportedOperationException();
     }
 
-    /*
-     * TODO(cpovirk): Uncomment the @NonNull annotations below once our JDK stubs and J2KT
-     * emulations include them.
-     */
     @Override
     @CheckForNull
-    /*
-     * Our checker arguably should produce a nullness error here until we see @NonNull in JDK APIs.
-     * But it doesn't, which may be a sign that we still permit parameter contravariance in some
-     * cases?
-     */
     public V computeIfPresent(
         K key, BiFunction<? super K, ? super @NonNull V, ? extends @Nullable V> remappingFunction) {
       throw new UnsupportedOperationException();