remove unused doc link

docs/modules/tutorials/nav.adoc

@@ -13,4 +13,3 @@
 *** xref:beginner/hello_audio.adoc[Hello Audio]
 *** xref:beginner/hello_effects.adoc[Hello Effects]
 *** xref:beginner/hello_physics.adoc[Hello Physics]
-*** xref:beginner/hellovector.adoc[Hello Vector3f]