Finalize cache size definitions in the code

[andrixnet]

Reading about this PR I realized there must be something wrong or incomplete. AFAIK cache size has been implemented in the code.
Further investigation yielded the following:

• 1) search.kml.inc.php still references cache_size table.
  in fact it seems to use translation defined by code, but a table join was left in the query
• 2) src/Utils/I18n/I18n.php
  lines 362 to end contain methods for retrieving and maintaining old-style database translations
• 3) src/Utils/Database/Updates/UpdateScript.php makes use of the code from the previous point.

To me it is apparent that the last dependency on DB definitions is 1) KML exporter.
Also, other then DB UpdateScript I could not find any reference translations still being used from DB.
If I am missing something, please add it to this issue.

Once that solved, components 2) and 3) may drop support for cache_size and the table can be dropped altogether from the database.