Remove the flag and make openTypedDocument throw FileNotFoundException.

To be compatible with ContentProvider, DocumentsProvider should not
require checking for a flag before calling openTypedAssetFile.

This CL removes the flag, and makes the default implementation throw
FileNotFoundException instead.

Bug: 26222645
Change-Id: I3492f05804e39583ebb8584109c7017b3082846e
9 files changed