powerpc/bpf: Remove bpf_jit_free()

Commit 74451e66 ("bpf: make jited programs visible in traces") added
a default bpf_jit_free() implementation. Powerpc did not use the default
bpf_jit_free() as powerpc did not set the images read-only. The default
bpf_jit_free() called bpf_jit_binary_unlock_ro() is why it could not be
used for powerpc.

Commit d53d2f78 ("bpf: Use vmalloc special flag") moved keeping
track of read-only memory to vmalloc. This included removing
bpf_jit_binary_unlock_ro(). Therefore there is no reason powerpc needs
its own bpf_jit_free(). Remove it.

Signed-off-by: Jordan Niethe <jniethe5@gmail.com>
Reviewed-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210609013431.9805-6-jniethe5@gmail.com