[!!!][TASK] Remove LinkHandler class in linkvalidator

Linkvalidator ships with several Linktype classes that are
used to check specific links such as ExternalLinktype,
Filelinktype etc.

The Linktype LinkHandler is not used by default (see
Page TSconfig mod.linkvalidator.linktypes).

It was used to check links of the extension "linkhandler"
which is now outdated. The latest version supports TYPO3
4.1.0. Functionality from the extension linkhandler has
been migrated to the core in TYPO3 8, but in any case
the LinkHandler link type supports outdated link syntax
starting with "record:".

Resolves: #92693
Releases: master
Change-Id: Ie0736720ce975b8ccf8e8323660e18d0c772b251
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/66265


Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>