Bug 11479: Remove experimental given/when keywords

Bug 11479: Remove experimental given/when keywords

Replace constructs using given and when by if/else
feature now generates compilation warnings in 5.18
and is liable to change behaviour.

This patch:

* replaces the construct with if/else
* reformats the if branching using perltidy
  to remove the now redundant indent

To test:

[1] Verify that prove -v t/db_dependent/MarcModificationTemplates.t
    passes.

Signed-off-by: Chris Cormack <chris@bigballofwax.co.nz>
Signed-off-by: Jonathan Druart <jonathan.druart@biblibre.com>
Signed-off-by: Galen Charlton <gmc@esilibrary.com>