fonts.md: change deprecated conf file to correct one

[flisakl]

Command for creating symlink used a deprecated file for disabling bitmap fonts.

Edit:
When you run:

fc-conflist | grep no-bitmap

you'll see:

[flisak@void] ~  $ fc-conflist | grep no-bitmap
+ /etc/fonts/conf.d/70-no-bitmaps-except-emoji.conf: Reject bitmap fonts except bitmap emoji fonts
- /usr/share/fontconfig/conf.avail/70-no-bitmaps-and-emoji.conf: Reject bitmap fonts, including bitmap emoji fonts
- /usr/share/fontconfig/conf.avail/70-no-bitmaps.conf: Reject bitmap fonts except bitmap emoji fonts (deprecated; use 70-no-bitmaps-except-emoji.conf)
[flisak@void] ~  $

[northboot]

Can confirm that the old symlink does not disable bitmap fonts anymore, confirmed by testing on wikipedia.org on Firefox.

[classabbyamp]

commit message should start with config/graphical-session/fonts: instead of fonts.md:

[flisakl]

I can't change commit message now. I've used format from CONTRIBUTING.md

The commit message should be in the form <filename>: <description_of_changes>.

I think it would be best to close this PR and @classabbyamp can apply the modification later, there's no point in making another PR or commit for such trivial change, but I am open to suggestions.