Remove project property from info

Merged Romanos Dodopoulos requested to merge rwmanos/adminimal-subtheme:master into master

The use of the project property is "discouraged and for packaging use only. Module maintainers should not use this at all".

Also, we have another (contrib) theme with the same project name defined which caused the following Drush error:

Error while trying to find the common path for enabled extensions of
project adminimal_theme. Extensions are: adminimal_theme,

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