This topic has been gone over many times. There is no need to remove rust inside the tubes. In most cases it’s never an issue. For the very anxious, there are internal coatings, such as framesaver that will stop the internal oxidation of steel tubing.

Many of us have frames over 50 years old that have never been the de-rusted or preserved on the inside, yet somehow we continue to ride them with no ill effects. There are outliers from bicycles that were stored outside near salty air, a.k.a. the ocean, that are more rusty than others. Even then, most have a lot of life left in them.