[공통][Common] 토스트 설정 변경 - 회색 배경 제거

app/src/main/res/layout/toast_simple.xml

@@ -3,7 +3,6 @@
   xmlns:android="http://schemas.android.com/apk/res/android"
   xmlns:app="http://schemas.android.com/apk/res-auto"
   xmlns:tools="http://schemas.android.com/tools"
-  android:background="@color/C999999"
   android:layout_width="match_parent"
   android:layout_height="match_parent">