Merge pull request #12036 from Carreau/cast_unicode-unused

remove unused import (cast_unicode)

IPython/core/inputsplitter.py

@@ -31,7 +31,6 b' import sys'
 import tokenize
 import warnings
 
-from IPython.utils.py3compat import cast_unicode
 from IPython.core.inputtransformer import (leading_indent,
                                            classic_prompt,
                                            ipy_prompt,