Voicemail provider: Don't automatically set HAS_CONTENT field.

It is best to let the content owner set this field when it is finished
writing the content into the file.

Another change will modify the voicemailproviderdemo app to set this
field in the app.

Bug: 5147190
Change-Id: I93e4b467acdefe339fa70dd751ea05f195c32e71
1 file changed