removed private use property from JotStylusManager header

The currentTouchesSet causes build warnings, specifically:

1. JotTouchSDK.framework/Versions/A/Headers/JotStylusManager.h:302:1: No 'assign', 'retain', or 'copy' attribute is specified - 'assign' is assumed
2. JotTouchSDK.framework/Versions/A/Headers/JotStylusManager.h:302:1: Default property attribute 'assign' not appropriate for non-GC object

removing the property from the public header does the trick, since its unused there anyways