Minor cleanup of Lanai code - unused code removal and comments correction

1) Remove unused NSRect and NSWindow from MTLGraphicsConfig.m _getMTLConfigInfo() method
2) MTLGraphicsConfig.java has a comment that indicates "getMTLConfigInfo() creates and destroys temporary surfaces/contexts," - it is not valid as we only create MTLContext in that method. This comment needs to be corrected.
3) Description comment of the abstract method - createSurfaceData() in CGraphicsConfig.java needs to specify both CGLLayer/MTLLayer as now we are implementing this method in both pipeline.