glsl: Remove unused field loop_variable_state::loop.

This field was neither initialized nor used.  It was just dead memory.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>

src/glsl/loop_analysis.h

@@ -70,11 +70,6 @@ public:
    class loop_terminator *insert(ir_if *);
 
 
-   /**
-    * Loop whose variable state is being tracked by this structure
-    */
-   ir_loop *loop;
-
    /**
     * Variables that have not yet been classified
     */