mesa: remove support for GL_APPLE_client_storage extension

AFAIK, there are few users of this extension and I can see a couple
reasons why this is probably broken in Mesa anyway.

Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>

src/mesa/main/teximage.c

@@ -610,7 +610,7 @@ _mesa_free_texture_image_data(struct gl_context *ctx,
 {
    (void) ctx;
 
-   if (texImage->Data && !texImage->IsClientData) {
+   if (texImage->Data) {
       /* free the old texture data */
       _mesa_free_texmemory(texImage->Data);
    }