[BUGFIX] require_once of vfsStream triggers travis fail

vfsStream is now included in ext:phpunit, the pear module is
not maintained and was removed in travis.
This triggeres a failure in the phplint check. All require_once
calls are removed for now, ext:phpunit now also provides an
autoloader for vfsSstream.

Change-Id: If1b07c31e999111e6b5d2804a9f5cc457066b7b0
Resolves: #50442
Releases: 6.2, 6.1, 6.0