Remove pointer to deprecated class page, from Skeleton3D

SkeletonIK3D is now deprecated, but Skeleton3D is recommending looking into its use for complicated inverse kinematics. What's worse, the removed line is not perfectly clear for non-developers and people less experienced with the engine, and could still stand to be improved.

(cherry picked from commit 0e52ffeb699f6d3a7164133912c7491d0b1c876f)

doc/classes/Skeleton3D.xml

@@ -7,7 +7,6 @@
 		[Skeleton3D] provides an interface for managing a hierarchy of bones, including pose, rest and animation (see [Animation]). It can also use ragdoll physics.
 		The overall transform of a bone with respect to the skeleton is determined by bone pose. Bone rest defines the initial transform of the bone pose.
 		Note that "global pose" below refers to the overall transform of the bone with respect to skeleton, so it is not the actual global/world transform of the bone.
-		To setup different types of inverse kinematics, consider using [SkeletonIK3D], or add a custom IK implementation in [method Node._process] as a child node.
 	</description>
 	<tutorials>
 		<link title="3D Inverse Kinematics Demo">https://godotengine.org/asset-library/asset/523</link>