perf record: Fix documentation for a inexistent option '-l'

'perf record' had a '-l' option that meant "scale counter values" a very
long time ago, but it currently belongs to 'perf stat' as '-c'.  So
remove it. I found this problem in the below case.

    $ perf record -e cycles -l sleep 3
      Error: unknown switch `l
Signed-off-by: Taeung Song <treeze.taeung@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: http://lkml.kernel.org/r/1507907412-19813-1-git-send-email-treeze.taeung@gmail.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/Documentation/perf-record.txt

@@ -8,8 +8,8 @@ perf-record - Run a command and record its profile into perf.data
 SYNOPSIS
 --------
 [verse]
-'perf record' [-e <EVENT> | --event=EVENT] [-l] [-a] <command>
-'perf record' [-e <EVENT> | --event=EVENT] [-l] [-a] -- <command> [<options>]
+'perf record' [-e <EVENT> | --event=EVENT] [-a] <command>
+'perf record' [-e <EVENT> | --event=EVENT] [-a] -- <command> [<options>]
 
 DESCRIPTION
 -----------