That isnt even a thing.
If it is someone’s theater you are a guest in they can tell you to say or not say whatever they want.
The idea anyway that a theater in 2019 is so poorly constructed that people are going to die by yelling fire is just stupid.
I was in a fairly empty theater last week, very old with a substandard elevator. Eleven of us were stuck inside for 20 minutes. Thankfully we all kept fairly calm and nobody yelled fire. It was the NYFD that got us out.