docs: remove llama_sampler_accept reference in sampling sample usage (#16920)

commit 5fb5e24811cb01d48b482c15a974bfbd9f433e1d (llama : minor
sampling refactor (2) (#9386)) moved the llama_sampler_accept call
into llama_sampler_sample, but the sampling sample usage in llama.h
was forgotten to be updated accordingly.