Revert "webpack: Use cache-loader for various loaders."

This reverts commit eb53b5e8de.

This appeared to not have the right logic yet for handling branch
switches.

See https://chat.zulip.org/#narrow/stream/3-backend/topic/frontend.20hot.20reloading/near/749259 for details.

tools/webpack-helpers.ts

@@ -1,13 +1,6 @@
-import { basename, resolve } from 'path';
+import { basename } from 'path';
 import { RuleSetRule } from 'webpack';
 
-export const cacheLoader: RuleSetRule = {
-    loader: 'cache-loader',
-    options: {
-        cacheDirectory: resolve(__dirname, '../var/webpack-cache'),
-    },
-};
-
 /* Return imports-loader format to the config
     For example:
     [
@@ -24,7 +17,7 @@ function getImportLoaders(optionsArr: ImportLoaderOptions[]): RuleSetRule[] {
     for (var loaderEntry of optionsArr) {
         importsLoaders.push({
             test: require.resolve(loaderEntry.path),
-            use: [cacheLoader, "imports-loader?" + loaderEntry.args],
+            use: "imports-loader?" + loaderEntry.args,
         });
     }
     return importsLoaders;
@@ -51,7 +44,7 @@ function getExposeLoaders(optionsArr: ExportLoaderOptions[]): RuleSetRule[] {
     for (var loaderEntry of optionsArr) {
         const path = loaderEntry.path;
         let name = "";
-        const useArr = [cacheLoader];
+        const useArr = [];
         // If no name is provided, infer it
         if (!loaderEntry.name) {
             name = basename(path, '.js');

tools/webpack.config.ts

@@ -4,7 +4,7 @@ import * as webpack from 'webpack';
 // The devServer member of webpack.Configuration is managed by the
 // webpack-dev-server package. We are only importing the type here.
 import * as _webpackDevServer from 'webpack-dev-server';
-import { getExposeLoaders, getImportLoaders, cacheLoader } from './webpack-helpers';
+import { getExposeLoaders, getImportLoaders } from './webpack-helpers';
 import * as MiniCssExtractPlugin from 'mini-css-extract-plugin';
 
 const assets = require('./webpack.assets.json');
@@ -42,13 +42,12 @@ export default (env?: string): webpack.Configuration => {
                 {
                     // We dont want to match admin.js
                     test: /(\.min|min\.|zxcvbn)\.js/,
-                    use: [cacheLoader, 'script-loader'],
+                    use: ['script-loader'],
                 },
                 // regular css files
                 {
                     test: /\.css$/,
                     use: getHotCSS([
-                        cacheLoader,
                         MiniCssExtractPlugin.loader,
                         {
                             loader: 'css-loader',
@@ -62,7 +61,6 @@ export default (env?: string): webpack.Configuration => {
                 {
                     test: /\.(sass|scss)$/,
                     use: getHotCSS([
-                        cacheLoader,
                         MiniCssExtractPlugin.loader,
                         {
                             loader: 'css-loader',