Remove position field from ITeamMembership

[pgrunewald]

Hello,

the position field is good for showing, that it is possible to add custom fields, but makes life hard when integrating (not everyone needs it in his/her setup). It is not required in order to maintain core functionality.

regards, Paul

[davisagli]

I would accept a pull request that removes it as long as it also includes clear documentation of how to re-add it to a custom workspace adapter.