In commit 2f15bd8c ("perf tools: Fix "Command" sort_entry's cmp and
collapse function") we switched from pointer to string comparison.

But failed to remove related comments. Removing them and adding another
one to warn before pointer comparison in here.
Signed-off-by: NJiri Olsa <jolsa@kernel.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20180206181813.10943-18-jolsa@kernel.orgSigned-off-by: NArnaldo Carvalho de Melo <acme@redhat.com>