lib, userdb-vpopmail: Fully remove var_expand_table_build()

It was accidentally removed in master-2.2 as part of the changes in
122014a

This finishes up the removal as it was done in master in
79fe1b2

src/auth/userdb-vpopmail.c

@@ -61,7 +61,10 @@ userdb_vpopmail_get_quota(const char *template, const char *vpop_str)
 	    strcmp(vpop_str, "NOQUOTA") == 0)
 		return "";
 
-	tab = var_expand_table_build('q', format_maildirquota(vpop_str), '\0');
+	tab = t_new(struct var_expand_table, 2);
+	tab[0].key = 'q';
+	tab[0].value = format_maildirquota(vpop_str);
+
 	quota = t_str_new(128);
 	var_expand(quota, template, tab);
 	return str_c(quota);

src/lib/var-expand.h

@@ -36,7 +36,4 @@ void var_get_key_range(const char *str, unsigned int *idx_r,
    If key is '\0', it's ignored. If long_key is NULL, it's ignored. */
 bool var_has_key(const char *str, char key, const char *long_key) ATTR_PURE;
 
-const struct var_expand_table *
-var_expand_table_build(char key, const char *value, char key2, ...);
-
 #endif