perf tools: Remove a write-only variable in the debugfs code

debugfs_premounted is written-to only so drop it. This functionality is
covered by debugfs_found now. Make it a bool while at it.

Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Link: http://lkml.kernel.org/r/1361374353-30385-2-git-send-email-bp@alien8.de


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>