matplotlib axes.clear() of twinx axes does not clear second y-axis label
<p>I have an issue with updated twinx axes.
In the following code, I expect that ax_hist.clear() clears data, ticks and axes labels altogether. But when I plot again in the same axes, second y-axis labels from the previous ax_hist.hist() are still there. 
How can I remove the old y-axis labels?</p>

<p>I have tested with TkAgg and Qt5Agg and got the same result.</p>

<pre><code>import matplotlib.pyplot as plt
import numpy as np

fig, ax = plt.subplots()

d1 = np.random.random(100)
d2 = np.random.random(1000)

ax.plot(d1)
ax_hist = ax.twinx()
ax_hist.hist(d1)

ax.clear()
ax_hist.clear()
ax.plot(d2)
ax_hist = ax.twinx()
ax_hist.hist(d2)
plt.show()
</code></pre>