remove comma on line 108

the original content is `AC_CHECK_HEADERS([sql.h, sqlext.h], [odbc_required_headers=yes], [odbc_required_headers=no])` on line 108 of file lib/odbc/configure.in, this will cause a compile error when test if the `sql.h` can be included in the method `ac_fn_c_try_compile` in the `lib/odbc/configure` script generated based on `lib/odbc/configure.in`.

Please check the `lib/odbc/config.log` file after running `configure` script in the ERL_ROOT dir.