transcoding: check API31 as it's available

bug: 178144708
test: unit tests; atest MediaTranscodeManagerTest
Change-Id: Idee97e5596bfe599fb294e7b71b50514ac941ead
diff --git a/media/libmediatranscoding/transcoder/VideoTrackTranscoder.cpp b/media/libmediatranscoding/transcoder/VideoTrackTranscoder.cpp
index b43efcb..7272a74 100644
--- a/media/libmediatranscoding/transcoder/VideoTrackTranscoder.cpp
+++ b/media/libmediatranscoding/transcoder/VideoTrackTranscoder.cpp
@@ -268,8 +268,7 @@
         return AMEDIA_ERROR_INVALID_PARAMETER;
     }
 
-// TODO: replace __ANDROID_API_FUTURE__with 31 when it's official (b/178144708)
-#define __TRANSCODING_MIN_API__ __ANDROID_API_FUTURE__
+#define __TRANSCODING_MIN_API__ 31
 
     AMediaCodec* encoder;
     if (__builtin_available(android __TRANSCODING_MIN_API__, *)) {