fix(build): removed never reached error handling

As theme override inclusions are always optional, LESS wont trigger an error in case the theme folder is not found.
We also moved the related code into a new overrides.less file (which still includes the files as optional), so fetching the import on error is never reached so the code can be safely removed.

tasks/config/tasks.js

@@ -9,7 +9,7 @@ let defaultBrowsers = browserslist(browserslist.defaults);
 let userBrowsers = browserslist();
 let hasBrowserslistConfig = JSON.stringify(defaultBrowsers) !== JSON.stringify(userBrowsers);
 
-var prefix = config.prefix || {};
+let prefix = config.prefix || {};
 if (!prefix.overrideBrowserslist && !hasBrowserslistConfig) {
     prefix.overrideBrowserslist = [
         'last 2 Chrome versions',
@@ -114,10 +114,7 @@ module.exports = {
                     let
                         regExp = {
                             variable: /@(\S.*?)\s/,
-                            theme: /themes[/\\]+(.*?)[/\\].*/,
-                            element: /[/\\]([^*/\\]*)\.overrides/,
                         },
-                        theme,
                         element
                     ;
                     if (error && error.filename && /theme.less/.test(error.filename)) {
@@ -127,10 +124,6 @@ module.exports = {
                                 console.error('Missing theme.config value for', element);
                             }
                             console.error('Most likely new UI was added in an update. You will need to add missing elements from theme.config.example');
-                        } else if (error.line === 84) {
-                            element = regExp.element.exec(error.message)[1];
-                            theme = regExp.theme.exec(error.message)[1];
-                            console.error(theme + ' is not an available theme for ' + element);
                         } else {
                             console.error(error);
                         }