Remove content replaced by new Learning Platform

[eddybrando]

Remove content replaced by new Learning Platform

[eddybrando]

The PR #3423 for the feature branch feat/sunset-learn-01 originally included the following list of tasks.

I'll be going through this list and checking if all of them are up-to-date because some changes has been made to qiskit.org since this feature branch started.

Remove the Learn with Qiskit section from the home page (#3418)

A similar change has already made its way into production (#3485). There is no need for further changes to achieve this.

Create a banner to announce the new Learning Platform (#3410)

The design of the banner in this feature branch is now outdated. The new design was introduced with #3495. The wording however might need to be changed.

Tasks:

• Replace banner old design with new design from production
• Change banner wording (included in #3555)

Create a banner to announce the new Learning Platform (Qiskit/platypus#2158)

This was already done in Qiskit/platypus#2180.

Remove the course "Understanding Quantum Information and Computation" (#3408)

Done in #3426.

Remove course "Variational Algorithm Design" (#3409)

Done in #3427.

Add the new learning platform link (#3422)

Marked as done in #3506.