Remove @J2ktIncompatible from Maps#immutableEnumMap

There are many enum collection APIs that don’t work on J2KT. But this here does
work fine.

RELNOTES=n/a
PiperOrigin-RevId: 608331195

Author: martinkretzschmar

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

@@ -151,7 +151,6 @@ V transform(Entry<K, V> entry) {
    * @since 14.0
    */
   @GwtCompatible(serializable = true)
-  @J2ktIncompatible
   public static <K extends Enum<K>, V> ImmutableMap<K, V> immutableEnumMap(
       Map<K, ? extends V> map) {
     if (map instanceof ImmutableEnumMap) {

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

@@ -156,7 +156,6 @@ V transform(Entry<K, V> entry) {
    * @since 14.0
    */
   @GwtCompatible(serializable = true)
-  @J2ktIncompatible
   public static <K extends Enum<K>, V> ImmutableMap<K, V> immutableEnumMap(
       Map<K, ? extends V> map) {
     if (map instanceof ImmutableEnumMap) {