[BUGFIX] Remove realpath call from unit test bootstrap

The calculation of PATH_site in TYPO3 does not
take the real location of the directory into
account but respects the settings of the webserver.

To avoid issues especially on Windows systems,
we need to remove the realpath call also from
the unit test bootstrap.

Releases: 6.2
Resolves: #52842
Change-Id: I4c5067e227aece444d4d9480b7ff758262c0996e
Reviewed-on: https://review.typo3.org/24790
Reviewed-by: Nicole Cordes
Tested-by: Nicole Cordes
Reviewed-by: Helmut Hummel
Tested-by: Helmut Hummel