Proposal: Remove REPL from Source §1 and Source §2

[martin-henz]

The REPL cannot be explained using the substitution model. You can't substitute an expression for a name in statements that haven't been entered yet by the user! So I propose we remove it from the workspaces when Source §1 or Source §2 are chosen.

The REPL relies on changes to the environment made in the previous query. In a way, it's a stateful construct. After removal of the REPL, students need to just put their test cases in the main program on the left. I think this is a reasonable price to pay for removing the magic of the REPL that we cannot explain to beginners.