docs: update syntax for date_part and extract functions in user guide

- Changed f.date_part(literal("month"), ...) to f.date_part("month", ...)
- Changed f.extract(literal("day"), ...) to f.extract("day", ...)

Author: kosiew

docs/source/user-guide/common-operations/functions.rst

@@ -77,8 +77,8 @@ Extracting parts of a date using :py:func:`~datafusion.functions.date_part` (ali
 .. ipython:: python
 
      df.select(
-        f.date_part(literal("month"), f.to_timestamp(col('"Total"'))).alias("month"),
-        f.extract(literal("day"), f.to_timestamp(col('"Total"'))).alias("day")
+        f.date_part("month", f.to_timestamp(col('"Total"'))).alias("month"),
+        f.extract("day", f.to_timestamp(col('"Total"'))).alias("day")
      )
   
 String