Avoid warnings in React >=16.3

[samkline]

Following up on #1407, there are two issues still causing warnings on the 5.x branch:

• In development, componentWillUpdate is used. Even though this is dev-only, it causes verbose warnings that can mask other issues when working in a large project.
• componentWillReceiveProps is incorrectly deleted from Connect's static properties, not from the prototype, so the delete is actually a no-op.

This PR addresses both issues. Thanks!

(This fixes an issue in an earlier PR I opened (#1409) -- I had gotten the lifecycle method wrong)

[timdorr]

Cool, thanks!