perf util: Kill die() prototype, dead for a long time

perf util: Kill die() prototype, dead for a long time

In fef2a735167a827a ("perf tools: Kill die()") the die() function was
removed, but not the prototype in util.h, now when building with
LIBPERL=1, during a 'make -C tools/perf build-test' routine test, it is
failing as perl likes die() calls and then this clashes with this
remnant, remove it.

Fixes: fef2a735167a827a ("perf tools: Kill die()")
Reviewed-by: Ian Rogers <irogers@google.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>