Note: Incorrect environment variable DISPLAY slows down startup (Gradio 3.28.2 and later)

[shirayu]

I have noticed that when I update sd-webui from 1.1.1 to 1.2.0 it takes a very long time to load the first time.
After investigation, I found that it was due to an incorrect setting of the DISPLAY environment variable.

With this commit, Gradio now calls matplotlib.get_backend().
However, an incorrect value for the DISPLAY environment variable is very time consuming.
(about 2 minutes in my environment).

I solved this problem by unset DISPLAY to delete the unnecessary DISPLAY environment variable.
This may not be relevant to most people, but I will leave a note here.