[resolver] only keep one preferred activity if selected with always=true

With this change, if user selects a preferred activity with "Always"
checked, there will only be one mAlways=true intent filter
for a given action.

BUG: 161394369
Test: manual
Test: atest FrameworksServicesTests
Change-Id: I3d5ee0130f6f07530bb53f9c1509d5121a46a34a