[grunt] remove custom uglify config

grunt/config/uglify.js

@@ -6,33 +6,8 @@ module.exports = {
       '<%= distDir %>/elasticsearch.jquery.min.js': '<%= distDir %>/elasticsearch.jquery.js'
     },
     options: {
-      compress: {
-        sequences: true,
-        properties: true,
-        dead_code: true,
-        drop_debugger: true,
-        unsafe: true,
-        conditionals: true,
-        comparisons: true,
-        evaluate: true,
-        booleans: true,
-        loops: true,
-        unused: true,
-        hoist_funs: true,
-        if_return: true,
-        join_vars: true,
-        cascade: true,
-        negate_iife: true,
-
-        pure_getters: false,
-        drop_console: false,
-        keep_fargs: false,
-        keep_fnames: false
-      },
       preserveComments: false,
-      screwIE8: true,
+      screwIE8: true
-      mangleProperties: true,
-      reserveDOMProperties: true
     }
   }
 };