fix: resolve IndexOutOfBounds error when removing images from top card (#6124)

replace deprecated onBackPressed with onBackPressedCallback

remove unit test for deprecated onBackPressed method

remove if-check before deleting picture to prevent hiding top thumbnail card

hide the thumbnail card on fragments other than MediaDetailFragment

Co-authored-by: Nicolas Raoul <nicolas.raoul@gmail.com>

app/src/test/kotlin/fr/free/nrw/commons/upload/UploadActivityUnitTests.kt

@@ -262,15 +262,4 @@ class UploadActivityUnitTests {
         method.isAccessible = true
         method.invoke(activity)
     }
-
-    @Test
-    @Throws(Exception::class)
-    fun testOnBackPressed() {
-        val method: Method =
-            UploadActivity::class.java.getDeclaredMethod(
-                "onBackPressed",
-            )
-        method.isAccessible = true
-        method.invoke(activity)
-    }
 }