hwmap_mediacodec_gl: detach surface texture from gl context on uninit
hwmap_mediacodec_gl: detach surface texture from gl context on uninit

Detaches the surface texture so it can re-attached later on. Fixes the
following runtime error:

[SurfaceTexture-0-3362-64] attachToContext: SurfaceTexture is already attached to a context

gopro/gopro-lib-node.gl,gopro/gopro-lib-node.gl,gopro/gopro-lib-node.gl,gopro/gopro-lib-node.gl