docs: remove agentName from skill.invoked event table

The runtime does not emit agentName on the skill.invoked event.
The agent name is used only for internal logging during eager
skill loading, not as event data.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: MackinnonBuck

docs/features/streaming-events.md

@@ -618,7 +618,6 @@ A skill was activated for the current conversation.
 | `allowedTools` | `string[]` | | Tools auto-approved while this skill is active |
 | `pluginName` | `string` | | Plugin the skill originated from |
 | `pluginVersion` | `string` | | Plugin version |
-| `agentName` | `string` | | Name of the agent that invoked the skill, when invoked by a custom agent |
 
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