Remove unused variables

ldap_mapper.c:842:15: warning: unused variable `i' [-Wunused-variable]
  unsigned int i;
               ^
ldap_mapper.c:841:35: warning: unused variable `der_len' [-Wunused-variable]
  size_t buf_len, user_filter_len, der_len;
                                   ^
ldap_mapper.c:840:17: warning: unused variable `der' [-Wunused-variable]
  unsigned char *der;
                 ^
Remove unused variables

ldap_mapper.c:906:8: warning: unused variable `bv_val' [-Wunused-variable]
  void *bv_val;
        ^
ldap_mapper.c:902:14: warning: unused variable `ber' [-Wunused-variable]
  BerElement *ber = NULL;
              ^
Remove unused variables

ldap_mapper.c: In function `ldap_mapper_match_user':
ldap_mapper.c:1210:6: warning: unused variable `i' [-Wunused-variable]
  int i=0;
      ^
Fix format error

ldap_mapper.c: In function `ldap_get_certificate':
ldap_mapper.c:1079:4: warning: format `%s' expects a matching `char *' argument [-Wformat=]
    DBG("ldap_first_entry() failed: %s");
    ^
Fix field precision specifier

ldap_mapper.c: In function `ldap_build_partial_cert_filter':
ldap_mapper.c:731:3: warning: field precision specifier `.*' expects argument of type `int', but argument 5 has type `long int' [-Wformat=]
   DBG2("ldap_build_cert_filter(): unrecognized certificate "
   ^
ldap_mapper.c:736:3: warning: field precision specifier `.*' expects argument of type `int', but argument 5 has type `long int' [-Wformat=]
   DBG2("ldap_build_cert_filter(): no values for certificate "
   ^
ldap_mapper.c:740:2: warning: field precision specifier `.*' expects argument of type `int', but argument 5 has type `long int' [-Wformat=]
  DBG4("ldap_build_cert_filter(): building subfilter '%.*s'='%.*s'",
  ^
ldap_mapper.c:740:2: warning: field precision specifier `.*' expects argument of type `int', but argument 7 has type `long int' [-Wformat=]