The dmabuf allocator in gl-renderer uses Mesa-specific code

The gl-renderer used to call official GL/ES APIs and worked with any GL implementation.

The dmabuf allocator, that was added to the gl renderer, unintentionally binds the gl-renderer to Mesa GL implementation by calling into Mesa-specific libs from the allocator code (and official GL API calls everywhere else). The allocator appears to be specifically created for the pipewire backend, the added functions are only called from the pipewire backend so the code should really be moved there.