Bug 12748: (QA followup) fix several tiny QA tools warnings

Bug 12748: (QA followup) fix several tiny QA tools warnings

  * admin/searchengine/elasticsearch/mappings.yaml:
    * Fix indentation so QA tools believe it's valid YAML
  * C4::AuthoritiesMarc: Remove tab character
  * C4::Search: Fix POD
  * Koha::BiblioUtils: remove "return undef"
  * Koha::Schema::Result::Search*: rename type to _type
  * Koha::SE::ES::Search:
    * Fix spelling/@_[0]
    * Add my to loop variable
    * Remove unused var $error
    * Add use Modern::Perl
    * Fix undefined variables
  * Koha::ES::Indexer: fix POD
  * Koha::SE::ES::QueryBuilder:
    * Don't define variables in conditionals
    * Fix POD
  * Koha::SE::Zebra::Search:
    * Fix debug warns/POD/barewords
    * Koha::SE::Zebra::Search: add use Modern::Perl
  * kohastructure.sql: remove old, unused elasticsearch_mappings table,
    add new tables
  * labels/label-item-search.pl: remove C4::Dates
  * opac/elasticsearch.pl: remove old file

Signed-off-by: Jesse Weaver <jweaver@bywatersolutions.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Brendan Gallagher <brendan@bywatersolutions.com>