Don't show new-window item in Downloads per Gabe.

Also, fix regression...don't show "internal storage" option in Downloads.
All other modes, fix inconsistencies in presentation of
internal-storage/new-windows commands by eliminating launch mode inference.
Update VolumeInfo and MTP provider to send correct launch mode extra.

Bug: 28691735,28695347
Change-Id: Ic480925f4c8f1beee4da104a2259c1ce5f28a6a1