perf hist: Remove the needless callchain.h include from hist.h

Nothing that is provided by callchain.h is used there, just things that
should've be directly included in hist.h, such as rbtree.h and a
map_symbol forward declaration.

Remove it so that we reduce the headers dependency tree.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: https://lkml.kernel.org/n/tip-zivvqfx93w5zzur7hr7h0nlh@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>