Fix compile time errors for objective-c using opengles
Fix compile time errors for objective-c using opengles

- Add missing __bridge keyword for void-pointer cast
- Remove context release which is no longer needed according to ARC standard
LWJGL-CI/bgfx,fluffyfreak/bgfx,mendsley/bgfx,jdryg/bgfx,jdryg/bgfx,emoon/bgfx,bkaradzic/bgfx,bkaradzic/bgfx,jpcy/bgfx,jpcy/bgfx,emoon/bgfx,jpcy/bgfx,mendsley/bgfx,LWJGL-CI/bgfx,emoon/bgfx,mendsley/bgfx,LWJGL-CI/bgfx,jpcy/bgfx,fluffyfreak/bgfx,fluffyfreak/bgfx,LWJGL-CI/bgfx,jdryg/bgfx,fluffyfreak/bgfx,bkaradzic/bgfx,jdryg/bgfx,bkaradzic/bgfx