chore: remove deprecated DualStack field

[njucjc]

- What I did I went through this deprecated field of net.Dial, which is DualStack. As described in the documentation of the net package:

// DualStack previously enabled RFC 6555 Fast Fallback // support, also known as "Happy Eyeballs", in which IPv4 is // tried soon if IPv6 appears to be misconfigured and // hanging. // // Deprecated: Fast Fallback is enabled by default. To // disable, set FallbackDelay to a negative value. DualStack bool

I think we don't need it anymore.

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