metal : remove memory pools (#15966)

metal : remove memory pools (#15966)

* metal : remove mem pool usage

ggml-ci

* metal : remove mem pool implementation

ggml-ci

* metal : take into account the actual allocated memory of the tensor

ggml-ci

* cont : use ggml_backend_buft_get_alloc_size

ggml-ci

* cont : improve, comments

ggml-ci

* cont : add functions for the extra tensor sizes

* metal : add comments

ggml-ci

* metal : implement .get_alloc_size for the rest of the buffer types

ggml-ci

* metal : remove ggml_metal_heap

ggml-ci