glx: directly link to gallium

this eliminates the loader interface, which avoids an entire class
of issues and simplifies a bunch of code

Acked-by: Daniel Stone <daniels@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/29771>

src/glx/dri2_glx.c

@@ -1058,7 +1058,7 @@ dri2CreateScreen(int screen, struct glx_display * priv, bool driver_name_is_infe
    }
    psc->driverName = driverName;
 
-   extensions = driOpenDriver(driverName, &psc->driver, driver_name_is_inferred);
+   extensions = driOpenDriver(driverName, driver_name_is_inferred);
    if (extensions == NULL)
       goto handle_error;
 
@@ -1178,8 +1178,6 @@ handle_error:
    psc->driScreen = NULL;
    if (psc->fd >= 0)
       close(psc->fd);
-   if (psc->driver)
-      dlclose(psc->driver);
 
    free(deviceName);
    glx_screen_cleanup(&psc->base);