[TASK] Remove unused property ReferenceIndex->WSOL

The public property in ReferenceIndex->WSOL was removed in 2006
and documented like that, but it has no effect, as it was never evaluated
since 14 years.

This property is removed, as the recommended way is to use the
->setWorkspaceId() anyway since a few years.

Resolves: #90217
Releases: master
Change-Id: Ib3b58c6823ec78cb0b51f19b104aa80186f0dfe6
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/63047


Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Reviewed-by: Oliver Hader <oliver.hader@typo3.org>
Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Oliver Hader <oliver.hader@typo3.org>