(1) Return a boolean instead of util::Status for methods in wv_cas_ecm.h

(2) Update wv_cas_ecm_example to NOT depend on ABSL

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=218884631

example/BUILD

@@ -48,8 +48,6 @@ cc_binary(
     srcs = ["wv_cas_ecm_example.cc"],
     deps = [
         "//base",
-        "@abseil_repo//absl/strings",
-        "//util:status",
         "//media_cas_packager_sdk/public:wv_cas_ecm",
     ],
 )