Remove unused method parameter

lib/gitlab/graphql/docs/helper.rb

@@ -74,7 +74,7 @@ module Gitlab
           render_row(render_name(value, enum[:name]), render_description(value, enum[:name], :inline))
         end
 
-        def render_union_member(union, member)
+        def render_union_member(member)
           "- [`#{member}`](##{member.downcase})"
         end
 

lib/gitlab/graphql/docs/templates/default.md.haml

@@ -126,7 +126,7 @@
   One of:
   \
   - type[:possible_types].each do |member|
-    = render_union_member(type, member)
+    = render_union_member(member)
   \
 
 :plain