patch 8.1.1007: using closure may consume a lot of memory

Problem:    Using closure may consume a lot of memory.
Solution:   unreference items that are no longer needed. Add a test. (Ozaki
            Kiichi, closes #3961)

src/version.c

@@ -779,6 +779,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1007,
 /**/
     1006,
 /**/