Update the depth & stencils chapter for GLFW 3.0

Hi, the chapter _Context Creation_ was updated for GLFW 3.0, but the code at the beginning of _Depth and Stencils_ is still for the old version.

GLFW 3.0 uses `glfwWindowHint()` to set depth and stencil bits, but the default value for depth bits is 24, and 8 for the stencil. So I think the whole paragraph is unnecessary now.

http://www.glfw.org/docs/latest/window.html#window_hints_values