Delete disconnected row when the corresponding remote file is deleted in a

MTP device.

The CL has MtpDatabase remove file metadata for the case.

1. Files app opens a MTP device. MtpDocumentsProvider stores the
   metadata of files in MtpDatabase.
2. A user disconnects the MTP device. MtpDatabase marks the files
   metadata as disconnected.
3. A user operates the MTP device and deletes a file in the MTP device.
4. A user connects the MTP device to Android again, and opens the MTP
   device again in Files app.
5. MtpDocumentsProvider updates the metadata of files, it should delete
   metadata of a file that was deleted at step 3.

BUG=27280143

Change-Id: I79b8df2457cd5b36d1706a9c6e3827c8e7d16208