perf scripting python: Assign perf_script_context

perf scripting python: Assign perf_script_context

The scripting_context pointer itself does not change and nor does it need
to. Put it directly into the script as a variable at the start so it does
not have to be passed on each call into the script.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Link: https://lore.kernel.org/r/20210530192308.7382-6-adrian.hunter@intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>