[BUGFIX] Ignore transient class loading info in composer mode

In composer mode, we must not register class loading information
on extension activation. It could make the extension work
for one request, but then fail in following requests, if
the class loading information is not properly provided by the extension
or the extension was not installed via composer.

Resolves: #70689
Releases: master
Change-Id: Ic039914e1f81b2c5d038530bfd994f176aa37501
Reviewed-on: http://review.typo3.org/44057


Reviewed-by: Alexander Grein <alexander.grein@gmail.com>
Tested-by: Alexander Grein <alexander.grein@gmail.com>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>
Reviewed-by: Andreas Fernandez <typo3@scripting-base.de>
Reviewed-by: Frank Nägler <frank.naegler@typo3.org>
Reviewed-by: Daniel Goerz <ervaude@gmail.com>
Tested-by: Daniel Goerz <ervaude@gmail.com>
Reviewed-by: Markus Klein <markus.klein@typo3.org>
Tested-by: Markus Klein <markus.klein@typo3.org>