Clean up test skips after KT-17137

We need to clean these up since primitive array `is` checks work now

(cherry picked from commit b413e9ef51606c51ebfb21bd7ff646b0fb75470a)

libraries/stdlib/test/collections/ArraysTest.kt

@@ -231,12 +231,6 @@ class ArraysTest {
     }
 
     @Test fun contentDeepToString() {
-        // Don't run this test unless primitive array `is` checks are supported (KT-17137)
-        if ((intArrayOf() as Any) is Array<*>) {
-            assertTrue(true)
-            return
-        }
-
         val arr = arrayOf("aa", 1, null, charArrayOf('d'))
         assertEquals("[aa, 1, null, [d]]", arr.contentDeepToString())
     }