Remove extra property

Gradle's ExtraPropertiesExtension is a commonly used mechanism for setting arbitrary key/value pairs on a project. This recipe removes every assignment of the property with the given key, whatever its value, such as ext.foo = 'bar', ext['foo'] = 'bar', ext.set('foo', 'bar'), an assignment in an ext { } block, or Kotlin's extra["foo"] = "bar" and val foo by extra("bar"). An ext { } block left empty is removed as well. Reads of the property are left as they are.