Remove dependency on eglplatform.h header

Fixes #636.

docs/compile.dox

@@ -281,6 +281,12 @@ available:
  - `_GLFW_USE_RETINA` to have windows use the full resolution of Retina displays
    (recommended)
 
+If you are using the EGL context creation API, the following options are
+available:
+
+ - `_GLFW_USE_EGLPLATFORM_H` to use `EGL/eglplatform.h` for native handle
+   definitions (fallback)
+
 @note None of the @ref build_macros may be defined during the compilation of
 GLFW.  If you define any of these in your build files, make sure they are not
 applied to the GLFW sources.