core: remove refcount for bpf program

core: remove refcount for bpf program

Currently ref count of bpf-program is kept in user space. However, the
kernel already implements its own ref count. Thus the ref count we keep for
bpf-program is redundant.

This PR removes ref count for bpf program as part of a task to simplify
bpf-program and remove redundancies, which will make the switch to
code-compiled BPF programs easier.

Part of #19270