return min amount of available custom variables across tables instead of maximum

core/Tracker/GoalManager.php

core/Tracker/Request.php

core/Tracker/TrackerCodeGenerator.php

core/Tracker/VisitorRecognizer.php

plugins/CoreAdminHome/Controller.php

plugins/CustomVariables/Archiver.php

plugins/CustomVariables/Commands/Info.php

plugins/CustomVariables/CustomVariables.php

...riables/tests/Commands/SetNumberOfCustomVariablesTest.php

...CustomVariables/tests/Integration/CustomVariablesTest.php

plugins/Live/Model.php

plugins/Live/Visitor.php