Do not generate a source map via postcss as it isn't included in the theme (#7335)

blockbase/assets/ponyfill.css

@@ -24,15 +24,15 @@ pre {
 * @param {string} hex - the hexadecimal value to convert
 * @return {string} comma separated rgb values
 */
-/**
- * Breakpoint mixins
- */
 /**
  * Long content fade mixin
  *
  * Creates a fading overlay to signify that the content is longer
  * than the space allows.
  */
+/**
+ * Breakpoint mixins
+ */
 /**
  * Focus styles.
  */
@@ -795,5 +795,3 @@ p.wp-block-site-tagline {
   color: var(--wp--custom--button--outline--hover--color--text, var(--wp--custom--button--color--text));
   background-color: var(--wp--custom--button--outline--hover--color--background, var(--wp--custom--button--color--background));
 }
-
-/*# sourceMappingURL=ponyfill.css.map */

blockbase/package.json

@@ -21,7 +21,7 @@
   "scripts": {
     "start": "chokidar \"sass/**/*.scss\" -c \"npm run build\" --initial",
     "build": "npm run build:scss",
-    "build:scss": "sass sass/ponyfill.scss assets/ponyfill.css --style=expanded --load-path ../node_modules && postcss assets/ponyfill.css --use autoprefixer --output assets/ponyfill.css --map"
+    "build:scss": "sass sass/ponyfill.scss assets/ponyfill.css --style=expanded --load-path ../node_modules && postcss assets/ponyfill.css --use autoprefixer --output assets/ponyfill.css --no-map"
   },
   "author": "Automattic",
   "license": "GPLv2"