Resolve errors in browser console caused by Instructor Dashboard

Description

This PR is to fix an annoying log that keeps showing in the browser's console when opening Instructor Dashboard:
![001](https://user-images.githubusercontent.com/17448993/84412877-8ba10680-ac18-11ea-9ea0-e7f071866d76.png)

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1- Related code for `InstructorAnalytics` has already been removed. This is causing TypeError to be logged:
![002](https://user-images.githubusercontent.com/17448993/84412887-8f348d80-ac18-11ea-8e06-1030b2462fe1.png)

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2- Instructor dashboard does not always show all supported tabs (for example, Certificate tab is not available when the the course doesn't include a certificate). This is causing `Uncaught Failed Element Selection` error to keep logged
![003](https://user-images.githubusercontent.com/17448993/84412901-93f94180-ac18-11ea-9366-71d6edbc3504.png)

Assignee

Unassigned

Reporter

Open Source Pull Request Bot

Labels

Contributor Name

Shadi Naif

Repo

edx/edx-platform

Customer

None

Epic Link

None

OSCM Assignee

None

Platform Map Area (Levels 1 & 2)

Educator Experiences - Course Operations

Platform Map Area (Levels 3 & 4)

None

Blended Hour Utilization Percentage

None

Priority

Unset
Configure