Don't remove SYSTEM_FIXED for intentional fixed grants to critical apps.

See b/208785537#comment11.

Bug: 208785537
Bug: 206556385
Bug: 183537857
Fixes: 203175819
Test: presubmit
Change-Id: Iaf5e2a0d86259805a9ef03f8f1baa14dd8c58da0
Merged-In: Iaf5e2a0d86259805a9ef03f8f1baa14dd8c58da0
(cherry picked from commit e6f07a4f)