Fix mypy linter check (#5185)

* Remove rdkit pin

Author: PardhavMaradani

.github/workflows/linters.yaml

@@ -93,7 +93,6 @@ jobs:
           micromamba: true
           full-deps: true
           numpy: numpy=1.26.0
-          rdkit: rdkit=2023.09.3
 
       - name: install
         run: |

package/MDAnalysis/lib/util.py

@@ -202,7 +202,7 @@
 import errno
 import functools
 import gzip
-import importlib
+import importlib.util
 import inspect
 import io
 import itertools