Add ability to remove elements from cbook.Grouper
Add ability to unshare a pair of shared [xy] axes

For example, let's say you shared a pair of x axes:

import matplotlib.pyplot as plt
fig = plt.figure()
ax1 = fig.add_subplot(1, 1, 1)
ax2 = fig.add_subplot(1, 1, 1, sharex=ax1)
ax1.plot(range(3))
ax2.plot(range(10))

You can then unshare the x axes shared between ax1 and ax2 like so

ax1.unshare_x_axes(ax2)

Alternatively, you can call

ax2.unshare_x_axes(ax1)

They are equivalent.
Reset adjustable for the passed axes
Only reset adjustable if there are no shared axes
Make shared axes a list instead of a Grouper