Create a new branch in mitodl/edx-platform for non plugin parts

[arslanashraf7]

Subtask of #3

Depends on #7

Background
We used to cherry-pick all the canvas integration-related code from mentioned commits in #3 before creating a plugin.

What needs to be done?
Now that we are moving the canvas integration into a pluggable app so in this ticket, we will create a new branch in https://github.com/mitodl/edx-platform where we should commit only that part of the commits mentioned in #3 which can't be moved to the plugin.

Acceptance Criteria:

• Remove canvas_integration dependency on remote_gradebook by moving required functionality to canvas_integration itself.
• Remove the remote_gradebook app Mentioned here
• Create a PR to the Maple branch in https://github.com/mitodl/edx-platform

[arslanashraf7]

Closed via mitodl/edx-platform#274