feat(content): weapon mount obsoletion, part 1

[yay855]

Purpose of change

Weapon mod mounts are a tedious and annoying mechanic, requiring you to craft a weapon mod to attach to a weapon in order to attach weapon mods to that weapon.

Describe the solution

All instances of weapon mod mounts in weapons have been replaced with a corresponding weapon mod. So for example, all stock mounts have been replaced with regular stock slots.
Furthermore, the weapon mod mount recipes have been obsoleted, and the weapon mod mount items have been moved to the obsolete folder.

Describe alternatives you've considered

We could make weapon mount mods easier to install, instead.

Testing

The json seems to have no errors, and given that it's a fairly simple change, it shouldn't spawn any errors

Additional context

Checklist

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[RoyalFox2140]

Okay so the one entire concern with this PR was what happened to the tests. Removing underbarrel_mount from the tests didn't invalidate them which means the mount does NOTHING besides add 10 grams of weight to a gun.

That means that if this is actually an egregious balance change it's solvable by adding said 10 grams of weight, but importantly, this does not affect gun stats or the tests would still be failing. There won't be unforeseen consequences here unless the tests failed to account for it.

[chaosvolt]

A lot of guns are affected by this, some of them we may wish to remove gunmod slots from later on, but the basic idea seems to be okay I guess. Mount slots seem to cause a lot of player confusion and I don't think I've seen any big pushback from others so far so hopefully this is aight.

I'm approving this but I may wish to ask for @scarf005 and especially @Coolthulhu to give their quick-and-dirty opinion on if they're okay with it too.