perf scripts python: exported-sql-viewer.py: Move report name into ReportVars

The report name is a report variable so move it into into ReportVars.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>