Fix SAM conversion generation condition

Remove check if array is passed to vararg parameter as it's not
relevant anymore and leads to ^KT-51821.

^KT-51821: Fixed

compiler/testData/codegen/box/sam/kt51821.kt

@@ -0,0 +1,11 @@
+fun interface A {
+    fun f(x: String): String
+}
+
+fun foo(a: A, vararg s: String): String =
+    a.f(s[0])
+
+fun bar(vararg s: String): String =
+    foo({ it }, s = s)
+
+fun box(): String = bar("OK")