Will eventually crash the editor or at least interfere with rendering as there will not be enough rendertexture resources to use

repro steps
1. Open Window > Analysis > Profiler
2. Enable memory module (profile modules drop down)
3. Under profile modules drop down, select "Memory" row
4. Set profiler to "Editor" (just left of record button)
5. In bottom window, change Simple > Detailed view
a. to see "Gather object references"
6. Get baseline
a. Click Take sample editor
b. View "Gather object references" tab
c. Examine Scene memory > renderTexture (memory used & ref count)
7. Paint with some texture brushes
a. Raise/lower terrain
b. Create new brush with mask filters (add, abs, etc..)
c. Transform > twist
d. Etc..
8. Update baseline (step 5) and compare

Expected results: Should not see increase in scene memory used or ref counts of scene memory objects