[CLEANUP] Cleanup Model/ClassObject.php

* Import classes
* Remove superfluous comments
  * Reason explained here: http://forge.typo3.org/issues/58248#note-1
* Fix wrong parameter types in phpdoc block
* Add missing parameters types in phpdoc block
* Methods should only have 1 return statement
* Fix if block style
* Add missing phpdoc block
* Remove unused local variables

Resolves: #58248
Releases: 6.2
Change-Id: I4ddd052abab7333d1ed46d4345664ab3a2b5d8f7
Reviewed-on: https://review.typo3.org/29684
Reviewed-by: Nico de Haen
Tested-by: Nico de Haen