Change ssl_sigalgs_from_value() to perform sigalg list selection.

Change ssl_sigalgs_from_value() to perform sigalg list selection.

Rather that passing in a sigalg list at every call site, pass in the
appropriate TLS version and have ssl_sigalgs_from_value() perform the
sigalg list selection itself. This allows the sigalg lists to be made
internal to the sigalgs code.

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