theme: Delete old themes.

Old theme format used in themes.py is deleted from this commit.

ZT_THEMES is changed to THEMES. `complete_and_incomplete_themes` is
edited to make it use the new THEMES instead of the old one.

tests/config/test_themes.py

@@ -40,37 +40,6 @@ def test_builtin_theme_completeness(theme_name):
     assert all(required_style in styles_in_theme for required_style in REQUIRED_STYLES)
 
 
-@pytest.mark.parametrize(
-    "theme_name, depth",
-    [
-        ("zt_dark", 16),
-        ("zt_dark", 256),
-        ("zt_light", 16),
-        ("zt_blue", 16),
-        ("gruvbox_dark", 16),
-        ("gruvbox_dark", 256),
-        ("gruvbox_dark24", 2 ** 24),
-        ("gruvbox_dark24", 2 ** 24),
-    ],
-)
-def test_migrated_themes(theme_name, depth):
-    def split_and_strip(style):
-        style = style.split(",")
-        style = [s.strip() for s in style]
-        return style
-
-    old_theme = THEMES[theme_name]
-    new_theme = generate_theme(theme_name.replace("24", ""), depth)
-    for new_style, old_style in zip(new_theme, old_theme):
-        assert new_style[0] == old_style[0]
-        if depth == 16:
-            assert split_and_strip(new_style[1]) == split_and_strip(old_style[1])
-            assert split_and_strip(new_style[2]) == split_and_strip(old_style[2])
-        else:
-            assert split_and_strip(new_style[4]) == split_and_strip(old_style[4])
-            assert split_and_strip(new_style[5]) == split_and_strip(old_style[5])
-
-
 def test_complete_and_incomplete_themes():
     # These are sorted to ensure reproducibility
     result = (