perf tools: Remove a trailing newline in the event terms

perf tools: Remove a trailing newline in the event terms

So that it can show the correct encoding info in the JSON output.

  $ perf list -j hw
  [
  {
          "Unit": "cpu",
          "Topic": "legacy hardware",
          "EventName": "branch-instructions",
          "EventType": "Kernel PMU event",
          "BriefDescription": "Retired branch instructions [This event is an alias of branches]",
          "Encoding": "cpu/event=0xc4/"
  },
  ...

Reviewed-by: Ian Rogers <irogers@google.com>
Suggested-by: Ian Rogers <irogers@google.com>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>