perf annotate browser: Compact 'nop' output

Just suppress the nop operands, future infrastructure that will record
the instruction lenght (and its contents) in struct ins will allow
rendering them as nopN, i.e. nop5 for a 5-byte nop.

Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Namhyung Kim <namhyung@gmail.com>
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-qddbeglfzqdlal8vj2yaj67y@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>