Coverity 1038133 fix

Clean up parsing code to suppress Coverity:
Dereference before null check (REVERSE_INULL)

Proper checking was already done.

src/detect-detection-filter.c

@@ -133,11 +133,8 @@ DetectThresholdData *DetectDetectionFilterParse (char *rawstr) {
         if(strstr(df_opt,"track"))
             track_found++;
     }
-
-    if (copy_str) {
     SCFree(copy_str);
     copy_str = NULL;
-    }
 
     if (count_found != 1 || seconds_found != 1 || track_found != 1)
         goto error;
@@ -207,8 +204,6 @@ error:
     }
     if (df != NULL)
         SCFree(df);
-    if (copy_str != NULL)
-        SCFree(copy_str);
     return NULL;
 }