Use build flag to safeguard virtual_camera service access

... in CameraProviderManager.

Bug: 318088136
Bug: 301023410
Test: locally enabling / disabling RELEASE_PACKAGE_VIRTUAL_CAMERA and
rebuilding
Test: atest CameraProviderManagerTest

Change-Id: I275fa268ea67365b968821112a9200e6cdb9fd5d
2 files changed