remove sparseCheckoutDir from the docs

[agiertli]

sparseCheckoutDir has been removed from the APi as per the:

#128

But it's still documented here:
https://devfile.io/docs/2.2.0/adding-projects#procedure
CTRL+F "sparseCheckoutDir"

Since this is no longer part of the API, it should be removed from the docs.

[kim-tsao]

Yes it should be removed. It looks like it got replaced by "subDir" but that's only available for starterProjects

[kim-tsao]

@mike-hoang can you take a look at this? We need to remove it for versions 2.0.0 and above