perf tests make: Remove the last egrep call, use 'grep -E' instead

perf tests make: Remove the last egrep call, use 'grep -E' instead

One last case, caught while testing with amazonlinux:2, centos:stream,
etc:

   4     7.28 amazonlinux:2                 : FAIL egrep: warning: egrep is obsolescent; using grep -E
gcc version 7.3.1 20180712 (Red Hat 7.3.1-17) (GCC)
   8    13.87 centos:stream                 : FAIL egrep: warning: egrep is obsolescent; using grep -E

Reviewed-by: Guilherme Amadio <amadio@gentoo.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: https://lore.kernel.org/lkml/ZUEdtblE8qDAQkBK@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>