Remove a project member

Removes a member, or leaves the project yourself.

Anyone may remove themselves, whatever their role: a colleague who no longer wants access should not have to ask for it, and leaving takes nothing from anybody else. Removing somebody else needs authority — an owner may remove anyone, an admin may remove a member and not another admin.

The owner's own row is refused: a project with no owner is unreachable, and the row names who pays. Removing the member a transfer is pending to withdraws the transfer.