perf ui: Make ui_browser__run exit on unhandled hot keys

Right now ENTER doesn't always exits the newt tree widget, as it is used
for expanding/collapsing branches, but with the new tree widget being
developed we need to regain control to handle it, expanding/collapsing
branches.

In fact its really up to the ui_browser user to state what extra keys
should stop ui_browser__run, and it should handle just the ones needed
for basic browsing.

Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>