Bug 13452: Fix obvious issues in issues_avg_stats.pl

Bug 13452: Fix obvious issues in issues_avg_stats.pl

- Remove joins with issuingrules which are not needed
- Fix the SQL query so that $weight is now the value of COUNT(*) instead
  of a timestamp
- QA fix: '$column eq $itype' instead of '$column =~ $itype' (same for
  $line)

Signed-off-by: Srdjan <srdjan@catalyst.net.nz>
Signed-off-by: Josef Moravec <josef.moravec@gmail.com>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
(cherry picked from commit 25d28e7c8100c1993f8794e39ed135781de04a47)
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>