Rwkv chat template fix (#10001)

* llama: remove useless template matching for rwkv-world

Signed-off-by: Molly Sophia <mollysophia379@gmail.com>

* converter: Add comment about the hack for rwkv models

Signed-off-by: Molly Sophia <mollysophia379@gmail.com>

* Update src/llama.cpp

Co-authored-by: Xuan Son Nguyen <thichthat@gmail.com>

---------

Signed-off-by: Molly Sophia <mollysophia379@gmail.com>
Co-authored-by: Xuan Son Nguyen <thichthat@gmail.com>