perf ui browser: Remove ui_browser__add_exit_keys

perf ui browser: Remove ui_browser__add_exit_keys

Users (hist_browser, etc) should just handle all keys, discarding the
ones they don't handle.

Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Mike Galbraith <efault@gmx.de>
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-fjouann12v2k58t6vdd2wawb@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>