bpf, arm: Remove dummy bpf_jit_compile stub

The BPF core defines a __weak bpf_jit_compile() dummy function already
which should only be overridden by JITs if they actually implement a
legacy cBPF JIT. Given arm implements an eBPF JIT, this stub is not
needed.

Now that MIPS cBPF JIT is finally gone, the only JIT left that is still
implementing bpf_jit_compile() is the sparc32 one.

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>