Make IAutofillManager fully oneway.

The critical methods on this interface - like updateSession() - were already
void, so all we had to do were to "onewaywize" the other methods. We could
either refactor them to be truly async, or implement a blocking mechanism that
let them still be sync *and* oneway - because these methods are not in the
critical path, we opted for the latter, which is simpler and less risky.

Fixes: 73536867

Test: mmma -j ./frameworks/base/apct-tests/perftests/autofill/ && \
      adb install -r $OUT/data/app/AutofillPerfTests/AutofillPerfTests.apk && \
      adb shell am instrument -w -e class android.view.autofill.LoginTest \
      com.android.perftests.autofill/android.support.test.runner.AndroidJUnitRunner
Test: CtsAutoFillServiceTestCases

Change-Id: I380430aa2a7805aed6f629afb360566fc5402abb