IR: work around a bug in interface delegation descriptors

interface I {
        fun f(x: Int = 1)
    }
    class C(val y: I) : I by y {
        // implicit `override fun f(x: Int) = y.f(x)` has a default value for `x`
    }

-- the only case where a function with overridden symbols has defaults.

compiler/testData/compileKotlinAgainstKotlin/delegatedDefault.kt

@@ -0,0 +1,17 @@
+// FILE: A.kt
+package lib
+
+interface A {
+    fun f(x: String = "OK"): String
+}
+
+class B : A {
+    override fun f(x: String) = x
+}
+
+class C(val x: A) : A by x
+
+// FILE: B.kt
+import lib.*
+
+fun box() = C(B()).f()