style: remove unused :require (#193)

Co-authored-by: Tienson Qin <tiensonqin@gmail.com>

src/main/frontend/components/datetime.cljs

@@ -4,7 +4,6 @@
             [frontend.components.svg :as svg]
             [frontend.date :as date]
             [frontend.state :as state]
-            [frontend.mixins :as mixins]
             [frontend.handler.repeated :as repeated]
             [frontend.handler.editor :as editor-handler]
             [cljs-time.core :as t]