ModelCheckpoint fails at garbage collecting checkpoint passed to Trainer.resume_from_checkpoint
🐛 Bug
When passing a checkpoint to Trainer via resume_from_checkpoint, it is not tracked/garbage collected by ModelCheckpoint class. Instead, a new checkpoint is instantiated and gargabe collected/updated as usual.

Please reproduce using the BoringModel and post here
https://colab.research.google.com/drive/1QJrLngpOZg1MOgAtZH5kRo_s6u-Hjh0n?usp=sharing
Expected behavior
Checkpoint passed to Trainer.resume_from_checkpoint is garbage collected.
If this is not desired behavior, I think a sentence or 2 should be added to the docs on the intended behavior.
Environment

CUDA:

GPU:

Tesla T4


available:         True
version:           10.1


Packages:

numpy:             1.18.5
pyTorch_debug:     True
pyTorch_version:   1.7.0+cu101
pytorch-lightning: 1.1.0
tqdm:              4.41.1


System:

OS:                Linux
architecture:

64bit



processor:         x86_64
python:            3.6.9
version:           #1 SMP Thu Jul 23 08:00:38 PDT 2020



Additional context
If this is due to epoch mismatching and not a design choice, #5007 #4655 #2401 could be possibly related.