Revert "perf pmu: Fix pmu events parsing rule"

As reported by Adrian Hunter, this breaks intel_pt event parsing:

  # perf record -e intel_pt//u uname
  event syntax error: 'intel_pt//u'
                               \___ parser error
  Run 'perf list' for a list of valid events

   Usage: perf record [<options>] [<command>]
      or: perf record [<options>] -- <command> [<options>]

      -e, --event <event>   event selector. use 'perf list' to list available events
  #

This reverts commit 9a4a931c

.

Reported-by: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: https://lkml.kernel.org/n/tip-ye1o2mji7x68xotiot1tn1gp@git.kernel.org
Signed-off-by: Arnaldo Carv...