Deduplicate span id from headers

[jbedell-newrelic]

Spec: https://source.datanerd.us/agents/agent-specs/pull/804

Sending the spanId has been deprecated. Regardless of whether an agent receives an inbound spanId value or not, agents MUST no longer send this value as part of the outbound tracestate header. If present on an inbound header, agents MUST still use this value but it is valid for this value to be missing. Ex: 190@nr=0-0-709288-8599547--164d3b4b0d09cb05-1-0.789-1563574856827.

[Newrelic-Boomi]

https://new-relic.atlassian.net/browse/NR-580795