Rely on numpy to properly normalize histograms with unequal bin widths #8333
Description
The source of hist contains the following snippets:
Notes
-----
Until numpy release 1.5, the underlying numpy histogram function was
incorrect with `normed`=`True` if bin sizes were unequal. MPL
inherited that error. It is now corrected within MPL when using
earlier numpy versions.
# hist_kwargs = dict(range=range, normed=bool(normed))
# We will handle the normed kwarg within mpl until we
# get to the point of requiring numpy >= 1.5.
and code for manual handling of the normed kwarg.
Given that we now require numpy >=1.7.1, we should just use the density kwarg to numpy.histogram to do this, and remove our own implementation.