Refactor: drop redundant list() wrapper around sorted() in formatter.py/text.py

## Summary

\`awscli/formatter.py:209-210\` (\`TableFormatter._group_scalar_keys_from_list\`) and \`awscli/text.py:91\` (\`_all_scalar_keys\`) wrap \`sorted(...)\` in \`list(...)\`, e.g. \`headers = list(sorted(headers))\`. \`sorted()\` already returns a \`list\`, so the wrapper is a needless no-op call.

## Proposed change

Drop the redundant \`list()\` wrapper in both locations: \`headers = sorted(headers)\`, \`more = sorted(more)\`, \`return sorted(keys_seen)\`. Pure refactor, no behavior change.

Open awscli/formatter.py at TableFormatter._group_scalar_keys_from_list and awscli/text.py at _all_scalar_keys. Confirm the three specified sorted() calls and remove only their redundant list() wrappers; done means the refactor is limited to those locations with no behavior change.

Written by the indexing model from the issue text.