[TF2] Fix the Third Degree's inconsistent behavior with Amputator healing

[Tkain]

Description

The Third Degree's current behavior with regard to players being healed by the Amputator taunt is inconsistent. Currently, as the TF2 wiki notes, when a Medic performs the Amputator taunt around a group of players:

• Attacking the taunting Medic with the Third Degree will damage the Medic only.
• Attacking a healing player with the Third Degree will damage the player and the taunting Medic only.

This PR fixes this inconsistency by not damaging the Amputator-taunting Medic when attacking a healing player with the Third Degree. This is done by not marking a healer as 'connected' to another player the healer's healing target is not also the player, which is only the case when they are being AoE healed.