[gitea] 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
(cherry picked from commit 5849d4fde347cd1e47f2243b3239724c73b1261d)

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',
@@ -110,12 +104,9 @@ export default {
       new EsbuildPlugin({
         target: 'es2020',
         minify: true,
-        css: !LightningCssMinifyPlugin,
+        css: true,
         legalComments: 'none',
       }),
-      LightningCssMinifyPlugin && new LightningCssMinifyPlugin({
-        sourceMap: sourceMaps === 'true',
-      }),
     ],
     splitChunks: {
       chunks: 'async',