[Input] remove extraneous props when using custom component

[rosskevin]

Fixes #7772

• PR has tests / docs demo, and is linted.
• Commit and PR titles begin with [ComponentName], and are in imperative form: "[Component] Fix leaky abstraction".
• Description explains the issue / use-case resolved, and auto-closes the related issue(s) (http://tr.im/vFqem).

[oliviertassinari]

I can't try this change right now as in the middle of a documentation rewrite of the infrastructure, but that looks good. Have you tried interacting with the demos?

[rosskevin]

No, tests pass and I found zero usages of input with custom component. I'm out now so I can't check anything probably until tomorrow.

[leoliu]

there are a few dozens of new entries to yarn.lock? What are they for?

[rosskevin]

I ran yarn because my local install was out of date. The package.json was unchanged so it should be of no consequence (and all tests pass). I have no idea why the lock ultimately changed, but I trust yarn to do that diff as well as our tests.

[rosskevin]

I figured this out. The Greenkeeper bot merges in changes but the yarn.lock isn't updated. Whenever one of us runs yarn locally, we'll see this reflected in the lock file.