Remove unused #include's from contrib, pl, test .c files

as determined by IWYU

Similar to commit dbbca2cf29, but for contrib, pl, and src/test/.

Reviewed-by: Alvaro Herrera <alvherre@alvh.no-ip.org>
Discussion: https://www.postgresql.org/message-id/flat/0df1d5b1-8ca8-4f84-93be-121081bde049%40eisentraut.org

contrib/ltree/ltree_io.c

@@ -10,7 +10,6 @@
 #include "crc32.h"
 #include "libpq/pqformat.h"
 #include "ltree.h"
-#include "utils/memutils.h"
 #include "varatt.h"
 
 

contrib/ltree/ltree_op.c

@@ -7,13 +7,11 @@
 
 #include <ctype.h>
 
-#include "access/htup_details.h"
-#include "catalog/pg_statistic.h"
 #include "common/hashfn.h"
 #include "ltree.h"
 #include "utils/builtins.h"
-#include "utils/lsyscache.h"
 #include "utils/selfuncs.h"
+#include "varatt.h"
 
 PG_MODULE_MAGIC;