DetectFlowintData - remove unused idx in TargetVar.

The idx inside TargetVar inside DetectFlowintData is never used, so remove
it.

src/detect-flowint.h

@@ -55,7 +55,6 @@ enum {
 
 /** If the target is another var, get the name and the idx */
 typedef struct TargetVar_ {
-    uint16_t idx;
     char *name;
 } TargetVar;