[glx-texture-pixmap] Don't enable the texture target when binding the texture

There's no need to enable the texture target unless it is going to be
used for rendering. Enabling it directly with glEnable calls confuses
Cogl's state caching.

This is a replacement for the patch in bug 1483 which was reverted.

clutter/glx/clutter-glx-texture-pixmap.c

@@ -134,8 +134,6 @@ texture_bind (ClutterGLXTexturePixmap *tex)
   if (!cogl_texture_get_gl_texture (cogl_tex, &handle, &target))
       return FALSE;
 
-  glEnable(target);
-
   /* FIXME: fire off an error here? */
   glBindTexture (target, handle);