Remove lightningcss (#29070)

Remove lightningcss and minify with esbuild again. The size of output
CSS will increase by around 1.4%, but I think it's worth it to allow
building gitea in more cases like the one in the linked issue. We can
reconsider once lightningcss becomes more stable.

Fixes: https://github.com/go-gitea/gitea/issues/29058

package.json

@@ -29,7 +29,6 @@
     "jquery": "3.7.1",
     "katex": "0.16.9",
     "license-checker-webpack-plugin": "0.2.1",
-    "lightningcss-loader": "2.1.0",
     "mermaid": "10.7.0",
     "mini-css-extract-plugin": "2.8.0",
     "minimatch": "9.0.3",

webpack.config.js

@@ -55,12 +55,6 @@ const filterCssImport = (url, ...args) => {
   return true;
 };
 
-// in case lightningcss fails to load, fall back to esbuild for css minify
-let LightningCssMinifyPlugin;
-try {
-  ({LightningCssMinifyPlugin} = await import('lightningcss-loader'));
-} catch {}
-
 /** @type {import("webpack").Configuration} */
 export default {
   mode: isProduction ? 'production' : 'development',
@@ -106,12 +100,9 @@ export default {
       new EsbuildPlugin({
         target: 'es2020',
         minify: true,
-        css: !LightningCssMinifyPlugin,
+        css: true,
         legalComments: 'none',
       }),
-      LightningCssMinifyPlugin && new LightningCssMinifyPlugin({
-        sourceMap: sourceMaps === 'true',
-      }),
     ],
     splitChunks: {
       chunks: 'async',