Add some missing "pre-placed" items to VC trader restock lists

[NovaRain]

Reference: https://docs.google.com/spreadsheets/d/1tee2YHRWjgus2tolCTeqAH4iiAd5yfyg9utXyw5FU20/edit?usp=sharing

The merchant boxes on VC maps have pre-placed items instead of being empty by default like the rest, but some items were not in the restock list in scripts. I see this as a dev oversight between mapping/scripting since there's really no telling if they're meant to be unique, unlike the .223 pistol in Eldridge's special stock and the first aid kit in Renesco's stock that are specifically scripted.

I also remove a duplicate entry in sishelf2.ssl, because from the comment Ripper is supposed to be a rare item in Buster's stock.

[burner1024]

Cool. I'd probably reduce chance for MKII items, and keep = instead of := to be consistent with other invocations.

[NovaRain]

By default (no inventory wipe) there are already mk2 items and it's possible to get better(?) metal armor, so I set mk2 leather the same restock chance as the basic one (higher than metal armors) to add some incentive (easier to buy more copies) to pick it for party members. Or maybe set it as the same chance as metal since the price is pretty close.

[burner1024]

Well, as you prefer.

[phobos2077]

Unless it's 100% probability, it's not a 1-to-1 fix for the pre-placed items. Since how wipe is implemented. Before these items would always be present when you trade for the first time. With non-100 probability, you might not see them.

[NovaRain]

At least now they have a chance to appear (like many other items in shops) instead of gone forever after the first wipe.