fix: remove unused flutter_localizations dependency

[stephenmcd]

pay and pay_android declared flutter_localizations as a dependency without importing or using it anywhere in lib/. Since it's an SDK package, its version is pinned to whatever intl version ships with the developer's installed Flutter SDK, which conflicts with apps that depend on a different intl version and breaks pub get/pub add pay for no functional benefit to the plugin.

Fixes #260

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