perf intel-pt: Remove no_force_psb from documentation

no_force_psb was dropped as a late change to the kernel driver.
Consequently, remove it from the documentation.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Link: http://lkml.kernel.org/r/1443089122-19082-2-git-send-email-adrian.hunter@intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>