perf tools: Rename parse_events__free_terms() to parse_events_terms__delete()

perf tools: Rename parse_events__free_terms() to parse_events_terms__delete()

To follow convention used in other tools/perf/ areas. Also remove the
need to check if it is NULL before calling the destructor, again, to
follow convention that goes back to free().

Cc: Alexei Starovoitov <ast@kernel.org>
Cc: He Kuang <hekuang@huawei.com>
cc: Jiri Olsa <jolsa@kernel.org>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Cc: Zefan Li <lizefan@huawei.com>
Cc: pi3orama@163.com
Link: http://lkml.kernel.org/n/tip-w6owu7rb8a46gvunlinxaqwx@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>