Remove unused SASS bundling script

This has been replaced by `buildCSS` from @hypothesis/frontend-build.

scripts/gulp/create-style-bundle.js

-'use strict';
-
-const fs = require('fs');
-const path = require('path');
-
-const autoprefixer = require('autoprefixer');
-const postcss = require('postcss');
-const postcssURL = require('postcss-url');
-const sass = require('sass');
-
-/**
- * @typedef Options
- * @prop {string} input - Input file path
- * @prop {boolean} minify - Whether to minify the generated bundle
- * @prop {string} output - Output file path
- */
-
-/**
- * Compile a SASS file and postprocess the result.
- *
- * @param {Options} options - Object specifying the input and output paths and
- *                  whether to minify the result.
- * @return {Promise} Promise for completion of the build.
- */
-async function compileSass({ input, minify, output }) {
-  const sourcemapPath = output + '.map';
-
-  let result = sass.renderSync({
-    file: input,
-    includePaths: [path.dirname(input), 'node_modules'],
-    outputStyle: minify ? 'compressed' : 'expanded',
-    sourceMap: sourcemapPath,
-  });
-
-  // Rewrite font URLs to look for fonts in 'build/fonts' instead of
-  // 'build/styles/fonts'
-  function rewriteCSSURL(asset) {
-    return asset.url.replace(/^fonts\//, '../fonts/');
-  }
-
-  const cssURLRewriter = postcssURL({
-    url: rewriteCSSURL,
-  });
-
-  const postcssPlugins = [autoprefixer, cssURLRewriter];
-  result = await postcss(postcssPlugins).process(result.css, {
-    from: output,
-    to: output,
-    map: {
-      inline: false,
-      prev: result.map.toString(),
-    },
-  });
-
-  fs.writeFileSync(output, result.css);
-  fs.writeFileSync(sourcemapPath, result.map.toString());
-}
-
-module.exports = compileSass;