message: Remove obsolete bn.js dependency from sdk
diff: "@iov/encoding": "^2.1.0",
  "@iov/utils": "^2.0.2",
  "axios": "^0.19.0",
  - "bn.js": "^5.1.1",
  "pako": "^1.0.11"
  },
  "devDependencies": {
  - "@types/bn.js": "^4.11.6",
  "@types/pako": "^1.0.1",
  "readonly-date": "^1.0.0"
  }
  