chore!: remove --env from llama stack run (#3711)

# What does this PR do?
user can simply set env vars in the beginning of the command.`FOO=BAR
llama stack run ...`

## Test Plan
Run
TELEMETRY_SINKS=coneol uv run --with llama-stack llama stack build
--distro=starter --image-type=venv --run




---
[//]: # (BEGIN SAPLING FOOTER)
Stack created with [Sapling](https://sapling-scm.com). Best reviewed
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[ReviewStack](https://reviewstack.dev/llamastack/llama-stack/pull/3711).
* #3714
* __->__ #3711

docs/docs/distributions/configuration.mdx

@@ -101,7 +101,7 @@ A few things to note:
 - The id is a string you can choose freely.
 - You can instantiate any number of provider instances of the same type.
 - The configuration dictionary is provider-specific.
-- Notice that configuration can reference environment variables (with default values), which are expanded at runtime. When you run a stack server (via docker or via `llama stack run`), you can specify `--env OLLAMA_URL=http://my-server:11434` to override the default value.
+- Notice that configuration can reference environment variables (with default values), which are expanded at runtime. When you run a stack server, you can set environment variables in your shell before running `llama stack run` to override the default values.
 
 ### Environment Variable Substitution
 
@@ -173,13 +173,10 @@ optional_token: ${env.OPTIONAL_TOKEN:+}
 
 #### Runtime Override
 
-You can override environment variables at runtime when starting the server:
+You can override environment variables at runtime by setting them in your shell before starting the server:
 
 ```bash
-# Override specific environment variables
-llama stack run --config run.yaml --env API_KEY=sk-123 --env BASE_URL=https://custom-api.com
-
-# Or set them in your shell
+# Set environment variables in your shell
 export API_KEY=sk-123
 export BASE_URL=https://custom-api.com
 llama stack run --config run.yaml