perf diff: Don't use hack to skip column length calculation

perf diff: Don't use hack to skip column length calculation

Previously we use a nasty hack to skip the hists__calc_col_len for block
since this function is not very suitable for block column length
calculation.

This patch removes the hack code and add a check at the entry of
hists__calc_col_len to skip for block case.

Signed-off-by: Jin Yao <yao.jin@linux.intel.com>
Reviewed-by: Jiri Olsa <jolsa@kernel.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Jin Yao <yao.jin@intel.com>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lore.kernel.org/lkml/20191107074719.26139-2-yao.jin@linux.intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>