## Description
- remove old error checking for an env file
- add a new message to indicate that a subshell is being created
## Test plan
```
suiop-cli [jkj/suiop-env-msg-fix] suiop env
> Select an environment: mysten/default/vultr-api
Starting a subshell with the environment set... exit the shell (usually ctrl-d) to exit the env
error This project's package.json defines "packageManager": "yarn@pnpm@9.1.1". However the current global version of Yarn is 1.22.22.
Presence of the "packageManager" field indicates that the project is meant to be used with Corepack, a tool included by default with all official Node.js distributions starting from 16.9 and 14.19.
Corepack must currently be enabled by running corepack enable in your terminal. For more information, check out https://yarnpkg.com/corepack.
done initializing 🎉
suiop-cli [jkj/suiop-env-msg-fix]
```
---
## Release notes
Check each box that your changes affect. If none of the boxes relate to
your changes, release notes aren't required.
For each box you select, include information after the relevant heading
that describes the impact of your changes that a user might notice and
any actions they must take to implement updates.
- [ ] Protocol:
- [ ] Nodes (Validators and Full nodes):
- [ ] gRPC:
- [ ] JSON-RPC:
- [ ] GraphQL:
- [ ] CLI:
- [ ] Rust SDK:
