[4.3] Loosened Symfony Version Constraints

A year ago, this probably would have been a bad idea, but symfony is now even more stable, and laravel is becoming less and coupled to the components (you rewrote the routing for 4,1, and I know you recently wripped out their database session stuff), to the point where I no longer think it makes sence to constrain the symfony component versions in the way we currently are.

In this pull, I've modified the versions constraints, and used `~2.3` and `~2.5` where I saw fit based on my knowledge of how laravel uses each of the components.

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Refs my comment in #5231 where we are bumping the symfony version in 4.3 for no real reason.