fix: remove Stream API polyfill (#1149)

examples/agent/openai-task.ts

examples/agent/react-task.ts

examples/tsconfig.json

packages/env/src/index.ts

packages/env/src/polyfill.ts

...maindex/e2e/examples/cloudflare-worker-agent/src/index.ts

packages/llamaindex/e2e/tsconfig.json

packages/llamaindex/src/agent/base.ts

packages/llamaindex/src/agent/react.ts

packages/llamaindex/src/agent/types.ts

packages/llamaindex/src/agent/utils.ts

packages/llamaindex/src/internal/utils.ts