Set pinner.pin_camera default to true.

This was set to false while we conducted an experiment last year,
and it concluded that this should be set to true.

Although we set the flag to true through Phenotype, there are
occasions where the flag isn't properly propagated, ending up
in an undesirad state. Setting it true by default will eliminate
such a race.

Test: adb shell dumpsys pinner
Bug: 184897981
Change-Id: I32db757cf915211978269dc4b836784d2052c6aa