If you go onto multiplayer, click on Pika's server, and click "Edit" instead of "Join" you can see an option to either make server resource packs always enabled, disabled, or ask you if you want to enable it when in-game.
Easiest way to disable it would be to put that option on "Disabled" and rejoin (You may have to restart your game if you were on OpLifesteal before disabling the resource pack)