Update DEMO_FILES for demos using EGL.

Update DEMO_FILES for demos using EGL.

Reflect the recent addtion of eglut and reorganization of the EGL demos.
This helps remove ~2k lines of duplicated code

$ git diff --shortstat -M 57cc1db87b5cacffd3344c49062c8289b7d46e78
 18 files changed, 298 insertions(+), 2178 deletions(-)