Remove needless emoji from migration guide note.
Remove needless emoji from migration guide note.

I added these emoji in 7f69cda445a44d7cfac144ba6e27da3c525117eb, but the
:bulb: emoji only renders in GitHub markdown, falling back to ugly/useless
text on the actual documentation page:
https://www.apollographql.com/docs/react/migrating/apollo-client-3-migration

Also, the robot arm is a relatively new unicode addition, so there's a
chance readers with older browsers won't be able to see that emoji
rendered correctly either: https://emojipedia.org/mechanical-arm/

apollographql/apollo-client,apollographql/apollo-client