docs: Minor textual cleanups in PR comments script

This commit applies minor textual updates to the
`scripts/gha/get_pr_review_comments.py` script:

- Removed an explanatory comment from the `import firebase_github` line
  for a cleaner import block.
- Refined the script's description in the command-line help text for
  slightly improved conciseness (removed an article "a").

Author: google-labs-jules[bot]

scripts/gha/get_pr_review_comments.py

@@ -18,7 +18,7 @@
 import argparse
 import os
 import sys
-import firebase_github # Assumes firebase_github.py is in the same directory or python path
+import firebase_github
 import datetime
 from datetime import timezone, timedelta
 
@@ -36,7 +36,7 @@ def main():
     default_repo = firebase_github.REPO
 
     parser = argparse.ArgumentParser(
-        description="Fetch review comments from a GitHub PR and format into a simple text output.",
+        description="Fetch review comments from a GitHub PR and format into simple text output.",
         formatter_class=argparse.RawTextHelpFormatter
     )
     parser.add_argument(