targets/pipe-loader: drop unused authentication

targets/pipe-loader: drop unused authentication

The dri, vdpau, omx, xvmc and gbm targets don't need any authentication
even the VL ones never used it. Either the respective loader or the
library itself (vl) is doing its auth prior to calling create_screen()

Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>
Acked-by: Matt Turner <mattst88@gmail.com>