Minor cleanup and improvements

[tylerhutcherson]

from @antonum

• Project ID doesn't need to be secret. Just use input()
• Don't ask for the region. Just use 'us-central1' as the default
• Skip user input for table name. Just use hackernews.
• Add a comment on what public table we are using and how to replace public hackernews with your own.
• Remove the last cell (!redis-stack-server stop). As is it doesn't work as expected and even an expected shutdown of Redis is not needed here. One can keep playing with the notebook after the "run all" is finished.
• For the same reasons as above - add a condition for cell 38 (delete tables), so the notebook is still usable for iterative development after "run all".
• Does it really need to be run on GPU runtime? Consider switching to CPU only.