qutebrowser: Remove blocked hosts from repo

Blocked hosts reside in a single (giant) plaintext file, which we
now remove from the repository.

Especially with the new blocking sources we grew from around 700k
(which was already a lot at ~35000 lines) to around 5MB which is
just stupid to keep in the git repo if we don't have to.
Since qutebrowser automatically re-creates the file for us on
running `:adblock-update` there's no reason to waste space here.

.gitignore

@@ -27,6 +27,8 @@ sponsorblock.txt
 /qutebrowser/.config/qutebrowser/stylesheets
 # ignore the generated readability file for webpages
 readability.html
+# ignore the adblock file generated by qutebrowser
+blocked-hosts
 
 # ignore vifm & ueberzug utility files
 vifm-help.txt