Raise priority of system handler for CHOOSER.

System chooser should always launch; 3p apps handling this intent
is not supported and not intended.

Bug: 156904978
Change-Id: I68e137e4f1d08a7f76c5718f41959a6dea80fc79
Test: manual - created + installed app that registers an
intent-filter for chooser; verified that this change prevents it
from elbowing its way into the flow.

Change-Id: I90c5175c4598fdeee33b8196c0996c9013e06158