themes: remove v_material temporarily

It is not ready now.

src/vconfigmanager.cpp

@@ -1170,8 +1170,11 @@ void VConfigManager::initThemes()
     m_themes.insert(VPalette::themeName(file), file);
     file = ":/resources/themes/v_pure/v_pure.palette";
     m_themes.insert(VPalette::themeName(file), file);
+
+    /* NOT ready yet. Wait for author's tuning.
     file = ":/resources/themes/v_material/v_material.palette";
     m_themes.insert(VPalette::themeName(file), file);
+    */
 
     // User theme folder.
     QDir dir(getThemeConfigFolder());