chore(papi): keep the upstream sources in upstream-src/

The pezkuwi-dev build treats any package with a src/ directory as its
own: it requires our license header on every file and builds it. These
are upstream files that must stay byte-identical to the source embedded
in dist/, so they live in upstream-src/ instead, which neither the build
nor the root tsconfig picks up.

packages/papi-utils/README.md

@@ -1,9 +1,9 @@
 # @pezkuwi/papi-utils
 
-**Source:** `src/` is [`@polkadot-api/utils`](https://www.npmjs.com/package/@polkadot-api/utils/v/0.2.0) 0.2.0 from
+**Source:** `upstream-src/` is [`@polkadot-api/utils`](https://www.npmjs.com/package/@polkadot-api/utils/v/0.2.0) 0.2.0 from
 [polkadot-api](https://github.com/polkadot-api/polkadot-api) (MIT), with imports of
 `@polkadot-api/*` renamed to `@pezkuwi/*`. `dist/` is its build;
-`scripts/check-papi-sources.mjs` fails CI unless the source embedded in `dist/` equals `src/`.
+`scripts/check-papi-sources.mjs` fails CI unless the source embedded in `dist/` equals `upstream-src/`.
 
 The upstream README follows.