remove deprecated traitlets shim (#14604)

codecov.yml

@@ -22,4 +22,3 ignore:
   - IPython/utils/localinterfaces.py
   - IPython/utils/log.py
   - IPython/utils/signatures.py
-  - IPython/utils/traitlets.py

pyproject.toml

@@ -348,7 +348,6 addopts = [
    "--ignore=IPython/utils/localinterfaces.py",
    "--ignore=IPython/utils/log.py",
    "--ignore=IPython/utils/signatures.py",
-   "--ignore=IPython/utils/traitlets.py",
    "--ignore=IPython/utils/version.py"
 ]
 doctest_optionflags = [