[TASK] Remove old class files in ext:extensionmanager

Remove old class files in ext:extensionmanager

Change-Id: I2c5589b0feb37b8608eae6241e0f6c35d61e9a38
Resolves: #51599
Releases: 6.2
Reviewed-on: https://review.typo3.org/23503
Reviewed-by: Oliver Klee
Reviewed-by: Kai Ole Hartwig
Tested-by: Kai Ole Hartwig
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn