Provide a way to "deactivate" the robotology-superbuild compiled from source

[traversaro]

Discussing with @Nicogene, it turns out that when a robotology-superbuild compiled from source with apt dependencies is added in the .bashrc of the system, and in a different terminal you want to work with conda, it would be convenient to have a way to "de-activate" the "robotology-superbuild environment" "activated" by the setup.sh scripts.

What I always suggested to people working with conda was to modify the .bashrc to remove the sourcing of the setup.sh of the robotology-superbuild, but sometimes people prefer to avoid that for the following reason:

• Because the laptop is a shared laptop, and they do not want to modify "shared" files like the .bashrc.
• Because they only need the conda environment in one terminal, while in the other terminals they need the usual robotology-superbuild compiled from source with apt dependencies.

fyi @martinaxgloria

[traversaro]

This feature is quite complex, I am afraid if we want to implement it, we would need to first work on #294 .