fix: remove pre-mature Deprecation notices

While the Master Key Provider and Master Key interfaces do not have a long term future,
they are still supported, and safe to use.

They will not be removed in version 3.x.
They MAY be removed in a future Major Version,
but only when AWS is preparing to release that new Major Version should AWS publish these deprecation notices.

Author: texastony

src/main/java/com/amazonaws/encryptionsdk/model/EncryptionMaterialsHandler.java

@@ -93,7 +93,6 @@ public List<String> getRequiredEncryptionContextKeys() {
     }
   }
 
-  @Deprecated
   public List<MasterKey> getMasterKeys() {
     if (materials != null) {
       return materials.getMasterKeys();