perf stat: Correct --no-aggr description

Description of --no-aggr in perf-stat man page is outdated. --no-aggr
can also be used while profiling specific set of cpus. For ex,

  $ perf stat -e cycles,instructions -C 1-2 --no-aggr -- sleep 1

    Performance counter stats for 'CPU(s) 1-2':

    CPU1   5,94,92,795   cycles
    CPU2   2,69,72,403   cycles
    CPU1   2,02,08,327   instructions   # 0.34 insn per cycle
    CPU2     73,17,123   instructions   # 0.12 insn per cycle

    1.000989132 seconds time elapsed
Signed-off-by: NRavi Bangoria <ravi.bangoria@linux.vnet.ibm.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/r/1490013438-5713-1-git-send-email-ravi.bangoria@linux.vnet.ibm.comSigned-off-by: NArnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/Documentation/perf-stat.txt

@@ -94,8 +94,7 @@ to activate system-wide monitoring. Default is to count on all CPUs.
 
 -A::
 --no-aggr::
-Do not aggregate counts across all monitored CPUs in system-wide mode (-a).
-This option is only valid in system-wide mode.
+Do not aggregate counts across all monitored CPUs.
 
 -n::
 --null::