Exclude Android System from being qualified for a role.

This change excludes the Android System from being qualified for a
role. Android System used to qualify for the dialer role in work
profile because when resolving intent as a work profile user, the
Android System offers IntentForwarderActivity as a potential choice
and was thus qualified according to the dialer role definition.

Bug: 110557011
Test: manual
Change-Id: Id8a5123607150b7df452f8ff61d17d46e9986201