Bug 28028: Remove misc/migration_tools/fix_onloan.pl

Bug 28028: Remove misc/migration_tools/fix_onloan.pl

There is an obvious error in the script since bug 23463 and it's known
to be broken for 10 years now (since bug 5579). As nobody complains we
can safely remove this script.

Signed-off-by: Joonas Kylmälä <joonas.kylmala@helsinki.fi>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
(cherry picked from commit c285de980266a23919fe64d26665ccd53355b820)
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>