mne.viz.plot_compare_evokeds should not draw colorbar legend when `legend=False`

When a colormap is passed to mne.viz.plot_compare_evokeds (for example cbar='viridis') it places a colorbar next to the axis (instead of a normal in-axis legend). While the presence of the standard legend can be controlled with legend=False, the colorbar legend is always drawn.

Example:

import numpy as np
import mne

info = mne.create_info(ch_names=list('ABCDE'), sfreq=50., ch_types='eeg')

conditions = ['cond1', 'cond2']
evokeds = dict()
for condition in conditions:
    data = np.random.random((5, 100)) * 1e-6
    evokeds[condition] = mne.EvokedArray(data, info, tmin=-0.25)

legend=False controls whether standard legend is drawn:

mne.viz.plot_compare_evokeds(evokeds)

mne.viz.plot_compare_evokeds(evokeds, legend=False)

However, when cbar argument is used, the colormap legend is always drawn:

mne.viz.plot_compare_evokeds(evokeds, cmap='viridis', legend=False)

I think legend=False should not plot the colorbar.

Start at the mne.viz.plot_compare_evokeds entry point and reproduce the issue with the example in the report, using a colormap and legend=False. Trace where the colorbar is created; done means legend=False suppresses both the standard legend and colorbar, while the colorbar remains available when legend is enabled.