sh-i18n--envsubst: retire unused string_list_member()

This static function has no callers, nor has it had any since its
introduction in ba67aaf2 (git-sh-i18n--envsubst: our own envsubst(1)
for eval_gettext(), 2011-05-14). Remove it.
Signed-off-by: NEric Sunshine <sunshine@sunshineco.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

sh-i18n--envsubst.c

@@ -237,18 +237,6 @@ string_list_sort (string_list_ty *slp)
     qsort (slp->item, slp->nitems, sizeof (slp->item[0]), cmp_string);
 }
 
-/* Test whether a string list contains a given string.  */
-static inline int
-string_list_member (const string_list_ty *slp, const char *s)
-{
-  size_t j;
-
-  for (j = 0; j < slp->nitems; ++j)
-    if (strcmp (slp->item[j], s) == 0)
-      return 1;
-  return 0;
-}
-
 /* Test whether a sorted string list contains a given string.  */
 static int
 sorted_string_list_member (const string_list_ty *slp, const char *s)