Remove react-is download hack (#26692)

This was added during an upgrade to Jest 24 in
#15778

By now we're at Jest 29. I think if CI passes we might not need this
hack anymore.

package.json

@@ -82,7 +82,6 @@
     "minimist": "^1.2.3",
     "mkdirp": "^0.5.1",
     "ncp": "^2.0.0",
-    "pacote": "^10.3.0",
     "prettier": "2.8.3",
     "pretty-format": "^29.4.1",
     "prop-types": "^15.6.2",
@@ -118,7 +117,7 @@
     "lint": "node ./scripts/tasks/eslint.js",
     "lint-build": "node ./scripts/rollup/validate/index.js",
     "extract-errors": "node scripts/error-codes/extract-errors.js",
-    "postinstall": "node node_modules/fbjs-scripts/node/check-dev-engines.js package.json && node ./scripts/flow/createFlowConfigs.js && node ./scripts/yarn/downloadReactIsForPrettyFormat.js",
+    "postinstall": "node node_modules/fbjs-scripts/node/check-dev-engines.js package.json && node ./scripts/flow/createFlowConfigs.js",
     "debug-test": "yarn test --deprecated 'yarn test --debug'",
     "test": "node ./scripts/jest/jest-cli.js",
     "test-stable": "node ./scripts/jest/jest-cli.js --release-channel=stable",