glDeleteFramebuffers() cannot be called directly for desktop GL
where we link to the GL library dynamically. It is also only
used from the ES2 code. Instead of adding additional #ifdef for
it, we just move it to grabTexture(), since deleting it from the
destructor, which is called from a different thread, is not valid
anyway.

It means we will create and destroy the ID every frame we capture,
but since it is just registering an ID, this should be fine.