perf hists: Don't format the percentage on hist_entry__snprintf

perf hists: Don't format the percentage on hist_entry__snprintf

We can't have color correctly set there because in libslang (and in a future
GUI) the colors must be set on a separate function call, so move that part to a
separate function and make the stdio fprintf function call it.

Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/n/tip-jpgy42438ce9tgbqppm397lq@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>