chore(*): don't define the grunt Yarn script

As opposed to npm, `yarn binName` invokes a binary named `binName` exposed
by the respective package so the `grant` Yarn script is no longer needed.

Author: mgol

package.json

@@ -16,8 +16,7 @@
   "scripts": {
     "commit": "git-cz",
     "test-i18n": "jasmine-node i18n/spec",
-    "test-i18n-ucd": "jasmine-node i18n/ucd/spec",
-    "grunt": "grunt"
+    "test-i18n-ucd": "jasmine-node i18n/ucd/spec"
   },
   "devDependencies": {
     "angular-benchpress": "0.x.x",