[Performance] Update ClockIndicator Plugin such that it takes a fixed amount of space

[unlikelyzero]

Is your feature request related to a problem? Please describe. At present, the header's clockindicator plugin is causing a reflow event on each tick. It's also shifting the header components dependent on the width of the clock's font-width.

[akhenry]

@unlikelyzero Can this be closed? Indicator appears to be removed.

[unlikelyzero]

@akhenry I only removed it from viper. Can't make changes against openmct#master yet