[TASK] Comment legacy files to be removed with 6.2

The 'old' class files before namespace switch are commented
to be removed with TYPO3 7.0, but they should be scheduled
for removal with 6.2.

Change-Id: I01bad5874d1bf57e4272f7918557a8f53213cd0e
Resolves: #43120
Releases: 6.0
Reviewed-on: http://review.typo3.org/16586
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn