Revert "FlxSpriteUtil: make most functions @:generic with type param, add @:noUsing to some"

This reverts commit 5506016207e4f7ca4d746c070dc0a4a392616573.
Merge branch 'dev' of https://github.com/HaxeFlixel/flixel into dev
FlxArrayUtil.intFromString() -> FlxStringUtil.toIntArray(), FlxArrayUtil.floatFromString() -> FlxStringUtil.toFloatArray()

Also add @:noUsing to some functins in FlxSpriteUtil