Fix incorrect usage of the isInstantApp

The #isInstantApp return true only if called by itself or by
somebody who can view instant apps or by somebody has has
been granted with access. Using the isInstantAppInternal with
system uid to bypass the visibility checks for the caller if
it is not neccessary in the function.

Bug: 203500958
Test: atest EphemeralTest
Test: atest InstantAppUserTest
Test: atest InstantAppTest
Test: atest PackageManagerTest
Change-Id: I48ead977bb125901832f387974a3679e20c6168d