Force classic ("auto") date converter in classic style.

... instead of the newfangled ConciseDateConverter.

This is specifically useful for running tests when one also has
`date.converter: concise` in their user-level matplotlibrc, as that
setting otherwise never gets overwritten by the test machinery, and
`test_figure.py::test_axes_removal` then fails (as it depends on
having `date.converter: auto`).

Author: anntzer

lib/matplotlib/mpl-data/stylelib/classic.mplstyle

@@ -232,6 +232,7 @@ date.autoformatter.hour   : %H:%M:%S
 date.autoformatter.minute : %H:%M:%S.%f
 date.autoformatter.second : %H:%M:%S.%f
 date.autoformatter.microsecond : %H:%M:%S.%f
+date.converter:                  auto  # 'auto', 'concise'
 
 ### TICKS
 # see http://matplotlib.org/api/axis_api.html#matplotlib.axis.Tick