removed duplicate import of datetime (#2134)

Author: PhilBrk8

pvlib/solarposition.py

@@ -22,7 +22,6 @@
 import pandas as pd
 import scipy.optimize as so
 import warnings
-import datetime
 
 from pvlib import atmosphere
 from pvlib.tools import datetime_to_djd, djd_to_datetime
@@ -587,7 +586,7 @@ def sun_rise_set_transit_ephem(times, latitude, longitude,
         # older versions of pyephem ignore timezone when converting to its
         # internal datetime format, so convert to UTC here to support
         # all versions.  GH #1449
-        obs.date = ephem.Date(thetime.astimezone(datetime.timezone.utc))
+        obs.date = ephem.Date(thetime.astimezone(dt.timezone.utc))
         sunrise.append(_ephem_to_timezone(rising(sun), tzinfo))
         sunset.append(_ephem_to_timezone(setting(sun), tzinfo))
         trans.append(_ephem_to_timezone(transit(sun), tzinfo))