Remove OKHighScoreChart.xcdatamodeld

Fix #10

When archiving a project that included OctopusKit, Xcode was spewing errors about "unexpected character in prerequisites" because of a `::` in `OctopusKit-master.d`

This was apparently caused by a naming conflict between OKHighScoreChart.xcdatamodeld and OKHighScoreChart.swift

Solution found at: AudioKit/AudioKit#2279 (comment)

Author: ShinryakuTako