Your Flight Manual will list all your equipment in that aircraft.
Yours should list the two comms - if you get ramped and they only find one, you will certainly be grounded.
An EO can be applied for to remove the unit for x amount of time and some conditions/limitations be made, like blanking the hole, placards and pulling and securing the CB.
In short having one of your two comms U/S is not breaching operations of the 20.18 requirements, but removing the unit is a completely different thing.
If you have an aircraft that has two turn and bank indicators and one is broken (stuck) you can not just remove the U/S one and keep flying around. It could be feeding information to other systems like the AP so now you start to get multiple failures or part failures. That's why you need an EO.