Use Zstd version string / function for phpInfo

[sergey-dryabzhinsky]

Not sure when it appeared in zstd:

// php_info_print_table_row(2, "Interface Version", buffer);
php_info_print_table_row(2, "Interface Version", ZSTD_versionString());
// or
php_info_print_table_row(2, "Interface Version", ZSTD_VERSION_STRING);