Fix Quickfix for missing operator adds infix modifier to created function (#1012)

Fixes #KT-14907

idea/testData/quickfix/createFromUsage/createFunction/binaryOperations/plusMissingArgs.kt.after

@@ -2,7 +2,7 @@
 
 class A<T>(val n: T) {
     fun plus(i: Int, s: String): A<T> = throw Exception()
-    infix operator fun plus(t: T): A<T> {
+    operator fun plus(t: T): A<T> {
         TODO("not implemented") //To change body of created functions use File | Settings | File Templates.
     }
 }