Google Photos Unlimited v4

• Fix Pixel-exclusive system services breaking: the module no longer hides pixel_experience_<year>_exclusive.xml sysconfig files system-wide on any device/ROM (#19)
• Remove the module's dependency on /system mounting: a metamount module (e.g. Magic Mount) is no longer needed on KernelSU Next 3.0.0+, since Pixel-exclusive features now applied entirely in-process
• Switch the default device profile to the original Pixel (non-XL), matching a real sailfish factory image build.prop (PPR1.180610.009, August 2018).
• Document that unlimited storage has to be verified on a newly backed-up photo, since Google Photos no longer reliably shows the storage tier in its settings (#18)