Remove gyp files from openmax_dl.

All clients should be on GN by now.

If you do use these, shout, and we can put them back.

Bug: none
Change-Id: Ic3b26200818140183b60603eceb36cbebaf03bb5
Reviewed-on: https://webrtc-review.googlesource.com/57163
Reviewed-by: Raymond Toy <rtoy@google.com>