Remove stray diff.

Author: Liam3851

pandas/compat/pickle_compat.py

@@ -17,7 +17,6 @@
 from pandas._libs.arrays import NDArrayBacked
 from pandas._libs.tslibs import BaseOffset
 
-from pandas.core.api import StringDtype
 from pandas.core.arrays import (
     DatetimeArray,
     PeriodArray,