RAM is not freed after the world is changed

[lukicdarkoo]

Steps to Reproduce

1. Load webots $WEBOTS_HOME/projects/robots/adept/pioneer3/worlds/pioneer3at.wbt (RAM usage should be around 326MB)
2. Open the spot.wbt sample (RAM usage should be around 1.1GB)
3. Load pioneer3at.wbt (you should see RAM usage to be around 1GB instead of ~326MB)

Expected behavior
The pioneer3at.wbt world should make the Webots use 326MB RAM after loading the spot.wbt world.

System

• Operating System: Linux Ubuntu 20.04
• Graphics Card: NVIDIA GeForce RTX 1070

[joachimhgg]

The issue is still occurring in the R2022a. When loading the worlds alternatively with two supervisors, we can observe that the memory is increasing, which confirm the memory leak.