Patch out Parental Controls detection and logging

We should remove the per-OS implementations of nsIParentalControlsService in /toolkit/components/parentalcontrols and always use the stubbed-out nsParentalControlsServiceDefault.cpp implementation.

When an implementation is present, URIs are sent to an isAllowed(... function that parental control software presumably can hook in the OS to filter content, and a log(...) method also takes in URIs.

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