Remove unused themes.default key in ko locale.
Remove unused themes.default key in ko locale.

vahnj/mastodon,vahnj/mastodon,glitch-soc/mastodon,Kirishima21/mastodon,vahnj/mastodon,Kirishima21/mastodon,Kirishima21/mastodon,vahnj/mastodon,im-in-space/mastodon,im-in-space/mastodon,glitch-soc/mastodon,im-in-space/mastodon,glitch-soc/mastodon,im-in-space/mastodon,glitch-soc/mastodon,Kirishima21/mastodon,vahnj/mastodon