SingletonHolder: Drop unused class

All classes which were using this have been migrated to hilt or object

Signed-off-by: Aayush Gupta <aayushgupta219@gmail.com>

app/src/main/java/com/aurora/store/data/SingletonHolder.kt

@@ -1,36 +0,0 @@
-/*
- * Aurora Store
- *  Copyright (C) 2021, Rahul Kumar Patel <whyorean@gmail.com>
- *
- *  Aurora Store is free software: you can redistribute it and/or modify
- *  it under the terms of the GNU General Public License as published by
- *  the Free Software Foundation, either version 2 of the License, or
- *  (at your option) any later version.
- *
- *  Aurora Store is distributed in the hope that it will be useful,
- *  but WITHOUT ANY WARRANTY; without even the implied warranty of
- *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
- *  GNU General Public License for more details.
- *
- *  You should have received a copy of the GNU General Public License
- *  along with Aurora Store.  If not, see <http://www.gnu.org/licenses/>.
- *
- */
-
-package com.aurora.store.data
-
-open class SingletonHolder<out T, in A>(private val constructor: (A) -> T) {
-
-    @Volatile
-    private var instance: T? = null
-
-    fun with(arg: A): T {
-        return when {
-            instance != null -> instance!!
-            else -> synchronized(this) {
-                if (instance == null) instance = constructor(arg)
-                instance!!
-            }
-        }
-    }
-}