Prevent popup windows during execution of latex_to_png_dvipng

[eendebakpt]

The exectution of latex_to_png_dvipng causes popup windows. This PR prevents that by setting flags to the subprocess.check_call.

Idea was suggested in https://github.com/jupyter/qtconsole/issues/542#issuecomment-1136297850

[MrMino]

@eendebakpt Can you add a whats-new entry describing the user-facing implications of this change?

See https://github.com/ipython/ipython/tree/master/docs/source/whatsnew/pr

[eendebakpt]

@

@eendebakpt Can you add a whats-new entry describing the user-facing implications of this change?

See https://github.com/ipython/ipython/tree/master/docs/source/whatsnew/pr

@MrMino Done.

One test is still failing. Perhaps not related to this PR. If it is, then I need some more information what is the problem

[eendebakpt]

@MrMino or @ccordoba12 You you review this PR once more please?

[eendebakpt]

@ccordoba12 Is there anything that needs to be done to merge this?