target/hppa: Remove object_class_is_abstract()

target/hppa: Remove object_class_is_abstract()

Since commit 3a9d0d7b64 ("hw/cpu: Call object_class_is_abstract()
once in cpu_class_by_name()"), there is no need to check if @oc is
abstract because it has been covered by cpu_class_by_name().

Signed-off-by: Gavin Shan <gshan@redhat.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-ID: <20231114235628.534334-3-gshan@redhat.com>
[PMD: Mention commit 3a9d0d7b64]
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>