perf string: Remove unused macro K()

Unused macro reported by [-Wunused-macros].

This macro is introduced to calculate the 'unit' size, in:

  d2fb8b4151a92223 ("perf tools: Add new perf_atoll() function to parse string representing size in bytes")

  8ba7f6c2faada3ad ("saner perf_atoll()")

This commit has simplified the perf_atoll() function and remove the
'unit' variable. This macro is not deleted, but nowhere else is using
it.

A single letter macro is confusing and easy to be misused.  So remove it
for code cleaning.

Signed-off-by: Chen Zhongjin <chenzhongjin@huawei.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Florian Fischer <florian.fischer@muhq.space>
Cc: Ian Rogers <irogers@google.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: John Garry <john.garry@huawei.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lore.kernel.org/lkml/20220926031440.28275-6-chenzhongjin@huawei.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
