docs(using-superpowers): drop dangling subagent-support anchor (#2010)

The prune in e7ddc25 removed the `## Subagent support` section from
antigravity-tools.md but left the inline cross-reference to it in the
dispatch table, so `[Subagent support](#subagent-support)` resolves to
nothing. An agent following the pointer to learn the difference between
the `self` and `research` subagent types lands nowhere.

Drop the dangling parenthetical. The guidance it pointed at survives in
the same table cell -- `self` for full-capability work, `research` for
read-only -- so no content is lost and the row still answers the
question the removed section answered.

gemini-tools.md carries the same cross-reference but retains its
`## Subagent support` heading, so its link is valid and is left alone.

Author: ferrous26

skills/using-superpowers/references/antigravity-tools.md

@@ -4,7 +4,7 @@ Skills speak in actions ("dispatch a subagent", "create a todo", "read a file").
 
 | Action skills request | Antigravity CLI equivalent |
 |----------------------|----------------------|
-| Dispatch a subagent (`Subagent (general-purpose):` template) | `invoke_subagent` with a built-in `TypeName` — `self` for full-capability work, `research` for read-only (see [Subagent support](#subagent-support)) |
+| Dispatch a subagent (`Subagent (general-purpose):` template) | `invoke_subagent` with a built-in `TypeName` — `self` for full-capability work, `research` for read-only |
 | Task tracking ("create a todo", "mark complete") | a **task artifact** — `write_to_file` with `IsArtifact: true` and `ArtifactType: "task"` (see [Task tracking](#task-tracking)). **Not** `manage_task`, which manages background processes. |
 
 ## Task tracking