Remove unnecessary inheritance

MidiIoWrapper's DataSourceUnwrapper doesn't need to inherit from
DataSourceBase, and removing that inheritance saves a little bit
of space too.

Test: build
Change-Id: I9f560ef57b76b624cf323d75872395a39f65ed1f
diff --git a/media/libmedia/MidiIoWrapper.cpp b/media/libmedia/MidiIoWrapper.cpp
index d8ef9cf..6d46363 100644
--- a/media/libmedia/MidiIoWrapper.cpp
+++ b/media/libmedia/MidiIoWrapper.cpp
@@ -17,7 +17,6 @@
 //#define LOG_NDEBUG 0
 #define LOG_TAG "MidiIoWrapper"
 #include <utils/Log.h>
-#include <utils/RefBase.h>
 
 #include <sys/stat.h>
 #include <fcntl.h>
@@ -50,7 +49,7 @@
     mDataSource = nullptr;
 }
 
-class DataSourceUnwrapper : public DataSourceBase {
+class DataSourceUnwrapper {
 
 public:
     explicit DataSourceUnwrapper(CDataSource *csource) {