perf tools: Remove strbuf_{remove,splice}()

No users, nuke them.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/n/tip-kfv2wo8xann8t97wdalttcx7@git.kernel.org


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>