Clean up MtpDatabase API.

Return MTP response codes instead of booleans for success or failure.
Remove some unused code.

Change-Id: I82ce80a4d7779233264e3caf139ebd0cece12f5c
Signed-off-by: Mike Lockwood <lockwood@android.com>
diff --git a/media/mtp/MtpDatabase.h b/media/mtp/MtpDatabase.h
index 7feb3dc..a17797e 100644
--- a/media/mtp/MtpDatabase.h
+++ b/media/mtp/MtpDatabase.h
@@ -54,14 +54,10 @@
     virtual MtpResponseCode         getObjectInfo(MtpObjectHandle handle,
                                             MtpDataPacket& packet) = 0;
 
-    virtual bool                    getObjectFilePath(MtpObjectHandle handle,
+    virtual MtpResponseCode         getObjectFilePath(MtpObjectHandle handle,
                                             MtpString& filePath,
                                             int64_t& fileLength) = 0;
-    virtual bool                    deleteFile(MtpObjectHandle handle) = 0;
-
-    virtual void                    beginTransaction() = 0;
-    virtual void                    commitTransaction() = 0;
-    virtual void                    rollbackTransaction() = 0;
+    virtual MtpResponseCode         deleteFile(MtpObjectHandle handle) = 0;
 };
 
 }; // namespace android