Connection: Move remote file upload handlers back to Jetpack class

[tyxla]

In #12699 we didn't port the remote media upload functionality to the connection package, but we moved a call to the responsible method in the connection manager 😱 You can see that there's a reference to $this->add_remote_request_handlers in the connection manager, but that method doesn't exist 😕

This PR puts the remote media upload initialization back to the Jetpack class where it belongs, as the method we're using still lives there. This is similar to what #13235 did for the JSON API auth.

Kudos to @brbrr for reporting that.

Changes proposed in this Pull Request:

• Connection: Move remote file upload handlers back to Jetpack class

Is this a new feature or does it add/remove features to an existing part of Jetpack?

• This is a continuation of this effort: p1HpG7-7lI-p2

Testing instructions:

• Apply this patch to your Jetpack on a connected site.
• Try uploading a file from Calypso to your site.

Proposed changelog entry for your changes:

• Connection: Move remote file upload handlers back to Jetpack class

[jetpackbot]

Thank you for the great PR description!

When this PR is ready for review, please apply the [Status] Needs Review label. If you are an a11n, please have someone from your team review the code if possible. The Jetpack team will also review this PR and merge it to be included in the next Jetpack release.

Scheduled Jetpack release: September 3, 2019.
Scheduled code freeze: August 27, 2019

Generated by 🚫 dangerJS against 9808fd4

[brbrr]

Works well in my tests! Thanks for the PR 🚢