Fix lite/debug CI [rebase and fixup into #15953]

Author: carmocca

tests/tests_app/core/scripts/lightning_overrides.py

@@ -10,7 +10,6 @@
     from pytorch_lightning import LightningDataModule, LightningModule, Trainer
     from pytorch_lightning.accelerators.accelerator import Accelerator
     from pytorch_lightning.callbacks import Callback
-    from pytorch_lightning.lite import LightningLite
     from pytorch_lightning.loggers import Logger
     from pytorch_lightning.loops import Loop
     from pytorch_lightning.plugins import PrecisionPlugin
@@ -49,9 +48,6 @@ class BoringLoop(Loop):
     class BoringMetric(Metric):
         pass
 
-    class BoringLightningLite(LightningLite):
-        pass
-
     class BoringFabric(Fabric):
         pass