Relax auto-launch checks for GET_CONTENT.

When a developer wraps an intent with Intent.createChooser(), they're
indicating that the user should always be prompted, instead of using
any "always use" defaults.  A recent CL changed the chooser behavior
to ensure that UI is always shown in the case where there is only one
match.

However, this caused us to start prompting for the GET_CONTENT intent,
for which there is only ever one DocumentsUI system app.  Since that
app delivers on the createChooser() contract described above, we're
okay automatically launching it.

Bug: 24464358
Change-Id: I0279d3343479c134a35f41ddf3cb4204d0ae6a90