[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: I2db757db54410c5764ab21aef90918a7771f2c92
Resolves: #43120
Releases: 6.0
Reviewed-on: http://review.typo3.org/16590
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn