Remove outdated matplotlib rcParams setting

Description

The legacy_colorbar setting has no effect in matplotlib 3.4+ - except that it gives a warning saying it's going to be removed. We now deploy offline calibration with matplotlib 3.4.2, so we can remove this line.

How Has This Been Tested?

I haven't tested; I'm trusting matplotlib's docs.

Types of changes

• Bug fix (non-breaking change which fixes an issue)

Checklist:

• My code follows the code style of this project.

Reviewers

@hammerd @danilevc

changed milestone to %3.4.3

added Waiting for review label

LGTM

merged

mentioned in commit 372c753f

removed Waiting for review label