Back to the Geneva Convention however:
Article 2 GPGC:
1..In addition to the provisions which shall be implemented in peace time, the present Convention shall apply to all cases of declared war or of any other armed conflict which may arise between two or more of the High Contracting Parties, even if the state of war is not recognized by one of them.
2..The Convention shall also apply to all cases of partial or total occupation of the territory of a High Contracting Party, even if the said occupation meets with no armed resistance.
3.. Although one of the Powers in conflict may not be a party to the present Convention, the Powers who are parties thereto shall remain bound by it in their mutual relations. They shall furthermore be bound by the Convention in relation to the said Power, if the latter accepts and applies the provisions thereof.
Article 3 GPGC.
1..Persons taking no active part in the hostilities, including members of armed forces who have laid down their arms and those placed hors de combat by sickness, wounds, detention, or any other cause, shall in all circumstances be treated humanely, without any adverse distinction founded on race, colour, religion or faith, sex, birth or wealth, or any other similar criteria. To this end the following acts are and shall remain prohibited at any time and in any place whatsoever with respect to the above-mentioned persons:
* violence to life and person, in particular murder of all kinds, mutilation, cruel treatment and torture;
* taking of hostages;
* outrages upon personal dignity, in particular, humiliating and degrading treatment;
* the passing of sentences and the carrying out of executions without previous judgment pronounced by a regularly constituted court affording all the judicial guarantees which are recognized as indispensable by civilized peoples.
Basically as long as the Taliban are considered Combatants (which they are) then we are subject to the Geneva Convention and they should be treated within its bounds, this includes not mutilating their bodies in the event of death.
We also have the Unlawful Combatant status, but that is not applied to the Taliban Fighters like it has been to al-Qaeda operatives and that is a legal minefield to say the least.
Article 2 does not apply to Iraq or Afghanistan any longer as there is an internationally recognised government in both, so only Article 3 applies now.
The highlighted bits you pasted for Article 3 only apply to live persons afaik and not dead ones.
Equally enemy Taliban do not fall under any of those definitions, they are not civilians, and they are also not members of armed forces due to lack of uniform