perf c2c: Change the default coalesce setup

Joe suggested to have the coalesce default set just to 'iaddr', because
it's easier to read on the default 'perf c2c report' output.

By removing the "pid" field from the default -c/--coalesce option, the
'perf c2c' report will group all the relevant PIDs under the instruction
address ('iaddr') bucket. User can always run "-c pid,iaddr" for a more
fine grained output on particular PIDs.

Suggested-by: Joe Mario <jmario@redhat.com>
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20181228101820.28010-1-jolsa@kernel.org


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>