Repro steps (case 1):
1. Create a new shader graph
2. Create a custom function node
3. Give the custom function node a float output
4. Plug the custom function node's output into the "color" output of the graph, observe the errors
5. Unplug the custom function node's output from the "color" output of the graph
Expected result: the error for the main preview is removed from the console
Actual result: the error for the main preview remains
Said error should look something like: "Shader error in 'Master': variable '_CustomFunction_d29bb6f5938242698c96d2462b742c1a_New_0' used without having been completely initialized at line 278 (on d3d11)"

Repro steps (case 2):
1. Create a new shader graph
2. Create a custom function node
3. Give the custom function node a float output, observe the error printed to the console
4. Delete the custom function node
Expected result: the error of the custom function node's preview failing to render is deleted when the custom function node is deleted
Actual result: the error stays

Repro steps (case 3):
1. Create a new shader graph
2. Create a custom function node
3. Give the custom function node a float output, observe the error printed to the console
4. Delete the output to the custom function node you just created
Expected result: the error of the custom function node's preview failing to render is deleted when the custom function node's preview shader changes
Actual result: the error stays

The errors for case 2 and 3 should look something like:
"Shader error in 'hidden/preview/CustomFunction_4d4dda8b932a414c9f04da5492c829d9': variable '_CustomFunction_4d4dda8b932a414c9f04da5492c829d9_New_0' used without having been completely initialized at line 145 (on d3d11)"