slstr_l2.yaml points to deleted slstr_l2.py

[ameraner]

Describe the bug
The PR #1410 (@adybbroe) removed slstr_l2.py, but did not update slstr_l2.yaml accordingly, which still points to now non-existing classes (see

satpy/satpy/etc/readers/slstr_l2.yaml

Line 14 in a109584

file_reader: !!python/name:satpy.readers.slstr_l2.SLSTRL2FileHandler

).

The PR comments discuss the similarity between the ghrsst_l2 and slstr_l2 readers, maybe the slstr_l2.yaml reader should be updated to point to the ghrsst_l2.py classes? Or, maybe even better, slstr_l2 shall be added to the list of renamed readers, see here

satpy/satpy/readers/__init__.py

Line 40 in a109584

PENDING_OLD_READER_NAMES = {'fci_l1c_fdhsi': 'fci_l1c_nc'}