glx/meson: use full include path for dri_interface.h

glx/meson: use full include path for dri_interface.h

Everything else uses `#include "GL/internal/dri_interface.h"` instead,
and this full path was even already used in other parts of GLX.

While at it, nothing uses `inc_gl_internal` anymore so let's remove it
as well.

Signed-off-by: Eric Engestrom <eric.engestrom@intel.com>
Reviewed-by: Dylan Baker <dylan@pnwbakers.com>
Tested-by: Clayton Craft <clayton.a.craft@intel.com>