EAS should never use .env.local for builds or updates

### Build/Submit details page URL

_No response_

### Summary

EAS 14 now loads `.env` file but it also uses `.env.local`, which is intended to be local-only environment variables, not for other environments.

### Managed or bare?

managed

### Environment

```
expo-env-info 1.2.2 environment info:
System:
OS: macOS 14.7.1
Shell: 5.9 - /bin/zsh
Binaries:
Node: 22.11.0 - ~/.nodenv/versions/22.11.0/bin/node
Yarn: 3.1.1 - ~/.nodenv/versions/22.11.0/bin/yarn
npm: 10.9.0 - ~/.nodenv/versions/22.11.0/bin/npm
Watchman: 2024.12.02.00 - /opt/homebrew/bin/watchman
Managers:
CocoaPods: 1.16.2 - /Users/colin/.rbenv/shims/pod
SDKs:
iOS SDK:
Platforms: DriverKit 24.2, iOS 18.2, macOS 15.2, tvOS 18.2, visionOS 2.2, watchOS 11.2
IDEs:
Xcode: 16.2/16C5032a - /usr/bin/xcodebuild
npmPackages:
babel-preset-expo: ~11.0.0 => 11.0.14
expo: ^51.0.39 => 51.0.39
react: 18.2.0 => 18.2.0
react-dom: 18.2.0 => 18.2.0
react-native: 0.74.5 => 0.74.5
react-native-web: ~0.19.6 => 0.19.12
npmGlobalPackages:
eas-cli: 14.4.1
Expo Workflow: managed

› npx expo-doctor
✔ Check package.json for common issues
✔ Check Expo config for common issues
✔ Check native tooling versions
✔ Check if the project meets version requirements for submission to app stores
✔ Check for common project setup issues
✔ Check dependencies for packages that should not be installed directly
✔ Check for app config fields that may not be synced in a non-CNG project
(node:99240) [DEP0040] DeprecationWarning: The `punycode` module is deprecated. Please use a userland alternative instead.
(Use `node --trace-deprecation ...` to show where the warning was created)
✔ Check for issues with Metro config
✔ Check npm/ yarn versions
✔ Check Expo config (app.json/ app.config.js) schema
✔ Check that packages match versions required by installed Expo SDK
✔ Check for legacy global CLI installed locally
✔ Check that native modules do not use incompatible support packages
✔ Check that native modules use compatible support package versions for installed Expo SDK

Didn't find any issues with the project!
```

### Error output

_No response_

### Reproducible demo or steps to reproduce from a blank project

With a `.env.local`

```sh
eas update --branch staging --message "blah"
[expo-cli] env: load .env.local
[expo-cli] env: export EXPO_PUBLIC_API_HOST EXPO_PUBLIC_WEBAPP_HOST
```

If `.env` file exists, it loads both.

In my case, it has updated local hosts in the staging builds because for some reason I don't configure these variables in eas.json (I may change that). But anyway, I believe `.env*.local` should strictly be limited to the local environment.