Remove FULLY_ASYNC mode from RemoteUploadMode enum

FULLY_ASYNC requires half-close support which is non-trivial to implement.
Remove it for now since NOWAIT_FOR_UPLOAD_COMPLETE provides the main benefit.

Author: brianduff

src/main/java/com/google/devtools/build/lib/remote/options/RemoteOptions.java

@@ -133,11 +133,6 @@ public enum RemoteUploadMode {
     WAIT_FOR_UPLOAD_COMPLETE,
     /** Block at the beginning of the next build waiting for upload completion. */
     NOWAIT_FOR_UPLOAD_COMPLETE,
-    /**
-     * Block at the beginning of the next build waiting for client-side upload completion, but don't
-     * wait for server acknowledgement. Data may be lost on transient failures.
-     */
-    FULLY_ASYNC,
   }
 
   /** Converter for {@link RemoteUploadMode}. */