b5130

metal : remove leftover ggml-metal.metal kernels file (#4051)

This commit removes the ggml-metal.metal file that used to contain all
the metal kernels. These have now been separated into separate kernels
in ggml/src/ggml-metal/kernels and it seems that this file was not
removed when synced with ggml.

This is currently preventing whisper.cpp to be released as the release
check fails.