Web.JSON: Remove original lockvar

I remove lockvar code from the Web.JSON because the code cause the
following exception

    Error detected while processing function ry)..<SNR>256_get_json..<SNR>257_import..<SNR>257__import..<SNR>257__build_module:
    line   27:
    E741: Value is locked: filter() argument

true/false/null tokens should be locked but this kind of strategy will
be prepared on Vital.vim thus I just remove the code.