Fix issue #204: Remove a poorly designed challenge

[Simon-Stone]

Fixes issue #204 by simply removing the challenge in question.

[github-actions]

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[martinosorb]

Thank you for taking care of this -- I agree that that exercise is poorly designed. However, I'm a bit hesitant on leaving this episode without any exercise. Would it be feasible to modify it so that e.g. it asks a simple question about the scope of variables in a code example like the one there?

[tobyhodges]

How about this?

:::::::::::::::::::::::::::::::::::::::  challenge

## Tracing Global Variables

The code block below is a repeat of the example above, 
but with a global variable called `temperature` defined 
before the `adjust` function definition.

```python
pressure = 103.9 
temperature = 294.15 # checkpoint 1

def adjust(t):
    temperature = t * 1.43 / pressure
    return temperature # checkpoint 2

print('adjusted:', adjust(0.9))
print('temperature after call:', temperature) # checkpoint 3
```

1. Think through the code block line-by-line, 
   tracing the value of the variables as the program is run. 
   Fill in the table with the values of variables 
   called `pressure`, `temperature`, and `t` 
   at each of the checkpoints (marked with comments in the code block). 
   Write "undefined" if the value of a variable has not yet been set.

    | Checkpoint | `pressure` | `temperature` | `t` |
    | ----------| ---------- | ------------- | ----------- |
    | 1          |            |               |     |
    | 2          |            |               |     |
    | 3           |            |               |     |
1. **Before running this code block,** think about what you expect the result to be. 
   Can you identify which of the options below is correct?
    1. A `NameError` again
    1. ```output
      adjusted: 0.01238691049085659
      temperature after call: 294.15
      ```
    1. ```output
      adjusted: 0.01238691049085659
      temperature after call: 0.01238691049085659
      ```
1. Now run the code. Did you predict the result correctly? 


:::::::::::::::  solution

After the global variables are first defined, 
their values are not modified by any of the subsequent lines.
No global variable called `t` is ever created outside the `adjust` function,
so this variable remains undefined at all of the checkpoints:

| Checkpoint | `pressure` | `temperature` | `t` |
| ----------| ---------- | ------------- | ----------- |
| 1          |     103.9       |      294.15         |  undefined   |
| 2          |     103.9       |      294.15         |  undefined   |
| 3          |     103.9       |      294.15         |  undefined   |

This means that the output produced by the code block is option 2:

```output
adjusted: 0.01238691049085659
temperature after call: 294.15
```

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