Don't automatically autofill when manual request returned just 1 dataset.

When the user manually requested autofill and the service returned just 1
dataset, the app was automatically filled with it.

The motivation here was that since the user explicitly asked for autofill,
it'd ok - and better for the user - to release the data to the app without
the selecting a dataset.

This assumption was ok initially, but now the API to manually request autofill
is public, so a malicious app could use to get autofill data without user
interation.

Test: CtsAutoFillServiceTestCases pass
Fixes: 62164695

Change-Id: I47c3d8c557533526572aa67a4240c0a57f54268d