Relocated sublime-request's packages.json into package_control_channel

I have added Sublime Text 3 support for `sublime-request`. In addition, to be a better Package Control citizen, I am relocating the `packages.json` information back into the `package_control_channel` repository (originally separated due to tags). In this PR:

- Removal of import from `sublime-request`'s `packages.json`
- Added `sublime-request` information to `package_control_channel`