This keyword will clear all variables added using the `EL Add Variable` keyword.

Example:

| `EL Add Variable`    |  var1            | hello                           |
| `EL Add Variable`    |  var2            | world                           |
| ${hw}=               | `EL Evaluate`    | $[join(' ', var1, var2)]        |
| `EL Clear Variables` |                  |                                 |
| `EL Evaluate`        | $[var1]          | *# fail none existing variable* |

=>

| ${hw} = 'hello world'
| # Would fail on second use of `EL Evaluate` since have used a variable that does not exist.
