chore(tokens): drop the unreachable sell branch from the swap success title

[bmc08gt]

Stacked on #1290 — base it there, not code/cash. Merge that first.

#1290 guts TokenInfoScreen.kt (-404 lines), taking the v1 ButtonOptions Sell button with it. That was the only place a SwapPurpose.Sell was ever constructed; the v2 action row offers Give, Convert, and Withdraw. So the swap-processing success title can no longer be reached as a sell.

That title's else arm existed to name the reserve for exactly that case:

is SwapPurpose.Convert -> state.destinationTokenName
is SwapPurpose.BalanceIncrease -> state.tokenName
else -> stringResource(R.string.title_cashReserves)

Now it catches only a sell that can't happen and a null purpose. This makes the two reachable purposes explicit and lets the fallback go unnamed rather than claim a destination it can't have — Fiat.formatted already takes a nullable suffix, so no signature change. title_cashReserves had no other reference and goes with it.

Deliberately left alone

• SwapPurpose.Sell and BalanceDecrease stay. Sell is unreachable but still referenced by SwapViewModel (5 sites), AppRoute.kt:226, and the still-routed TokenSellReceiptScreen, plus two tests. Deleting the type is a much wider change than this one — worth its own PR. BalanceDecrease is also implemented by Convert.
• canSell stays — it's a computed property the Convert flow reads at TokenInfoViewModel.kt:336 to gate the "no balance yet" bottom bar.
• action_sell stays — still used by TokenSellReceiptScreen.kt:74.

Conflict note

feat/usdc-to-dollars-conversion-graphic (commit 602ac8960) touches this same when to suppress the "of " suffix for non-Flexible Buy and reserve-bound Convert. Both changes converge on a nullable suffix, so resolution is mechanical — keep that branch's Buy/Convert arms and this branch's dropped sell fallback.