This fixes 10 of our Xcode warnings:
- `MessageReactionPicker.swift` was declaring a variable and not using
it, leading to "Immutable value 'emoji' was never used". I simply
removed it.
- `Stripe.swift` had a bunch of unnecessary `public`s, which caused
"'public' modifier is redundant for static property declared in a
public extension".
- `SubscriptionManager.swift` had an unnecessary `try`, causing "No
calls to throwing functions occur within 'try' expression".
- `CallService.swift:696` was calling a function and not using its
result, so I annotated that function with `@discardableResult`.
- `MobileCoinAPI+Configuration.swift` declared a variable with `var`
that should've used `let`.
Nothing major here, but wanted to find ones that were easy to fix.
67ea0d0516